[Asus Zenpad 8.0 Questions & Answers] diplomatic:
No, this is not another thread asking about root methods for the Z380M. I actually have some useful information here.

The Asus stock firmware sucks big time. And the bootloader cannot be unlocked. But fortunately, there seems to be a way to flash a custom boot and recovery images, or anything you want into any location.

The Z380M (and its cousin Z300M) is a Mediatek device that allows easy access to the SoC's Meta mode over USB. I won't go into details about what that is or how to use SP Flash Tool. That is all public information. I'll just get straight to the point.

To boot to meta mode, with the tablet powered off, hold down Volume Up while you plug in the USB cable. Of course you have to have Flash Tool waiting for the device on your PC at this point. While you can use any version of SPFT v5 to read back data, the only version SPFT that works for flashing ("downloading") is v5.1532. This will let you flash a custom recovery or custom boot image (kernel). I'm posting a scatter file for this device.

Now of course the bootloader is permanently locked. So that means it verifies the signature of any boot or recovery image before it starts it. But that's not the end of the world. As far as I can tell, it still lets you boot custom images that have some signature on them (i.e. self-signed), not necessarily the OEM's. The bootloader merely warns you about Android's Yellow boot state at the logo screen, but lets you continue booting. I tested this by deliberately corrupting the boot image's signature.

Of course, this capability makes rooting the stock ROM trivial. But what I would really like to have is TWRP for this tablet. And I think so would a lot of people. And I would love to have a custom ROM on it that's closer to Android AOSP. The kernel source is up on Asus's site. So someone please get on that. :D

Now a bit of warning: the first time you flash something with SPFT, it may corrupt your partition table. That's why you should make a complete backup before you flash anything. SPFT has a habit of resizing the userdata partition for some reason. But this updated scatter file should prevent that from happening.

Asus Z380M scatter file:

############################################################################################################
#
# General Setting
#
############################################################################################################
- general: MTK_PLATFORM_CFG
info:
- config_version: V1.1.2
platform: MT8163
project: asus8163_tb_380_m
storage: EMMC
boot_channel: MSDC_0
block_size: 0x20000
############################################################################################################
#
# Layout Setting
#
############################################################################################################
- partition_index: SYS0
partition_name: PRELOADER
file_name: preloader_asus8163_tb_380_m.bin
is_download: true
type: SV5_BL_BIN
linear_start_addr: 0x0
physical_start_addr: 0x0
partition_size: 0x40000
region: EMMC_BOOT_1
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: BOOTLOADERS
d_type: FALSE
reserve: 0x00

- partition_index: SYS1
partition_name: pgpt
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0x0
physical_start_addr: 0x0
partition_size: 0x80000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS2
partition_name: proinfo
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0x80000
physical_start_addr: 0x80000
partition_size: 0x300000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: PROTECTED
reserve: 0x00

- partition_index: SYS3
partition_name: nvram
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0x380000
physical_start_addr: 0x380000
partition_size: 0x500000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: BINREGION
reserve: 0x00

- partition_index: SYS4
partition_name: protect1
file_name: NONE
is_download: false
type: EXT4_IMG
linear_start_addr: 0x880000
physical_start_addr: 0x880000
partition_size: 0xa00000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: PROTECTED
reserve: 0x00

- partition_index: SYS5
partition_name: protect2
file_name: NONE
is_download: false
type: EXT4_IMG
linear_start_addr: 0x1280000
physical_start_addr: 0x1280000
partition_size: 0xa00000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: PROTECTED
reserve: 0x00

- partition_index: SYS6
partition_name: asus_nvm
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0x1c80000
physical_start_addr: 0x1c80000
partition_size: 0x100000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: BINREGION
reserve: 0x00

- partition_index: SYS7
partition_name: persist
file_name: NONE
is_download: false
type: NONE
linear_start_addr: 0x1d80000
physical_start_addr: 0x1d80000
partition_size: 0x2000000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS8
partition_name: seccfg
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0x3d80000
physical_start_addr: 0x3d80000
partition_size: 0x40000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS9
partition_name: lk
file_name: lk.bin
is_download: true
type: NORMAL_ROM
linear_start_addr: 0x3dc0000
physical_start_addr: 0x3dc0000
partition_size: 0x80000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS10
partition_name: boot
file_name: boot.img
is_download: true
type: NORMAL_ROM
linear_start_addr: 0x3e40000
physical_start_addr: 0x3e40000
partition_size: 0xff7000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS11
partition_name: recovery
file_name: recovery.img
is_download: true
type: NORMAL_ROM
linear_start_addr: 0x4e37000
physical_start_addr: 0x4e37000
partition_size: 0xff7000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS12
partition_name: secro
file_name: secro.img
is_download: true
type: EXT4_IMG
linear_start_addr: 0x5e2e000
physical_start_addr: 0x5e2e000
partition_size: 0xff7000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS13
partition_name: para
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0x6e25000
physical_start_addr: 0x6e25000
partition_size: 0x80000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS14
partition_name: logo
file_name: logo.bin
is_download: true
type: NORMAL_ROM
linear_start_addr: 0x6ea5000
physical_start_addr: 0x6ea5000
partition_size: 0x800000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS15
partition_name: expdb
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0x76a5000
physical_start_addr: 0x76a5000
partition_size: 0xa00000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS16
partition_name: frp
file_name: NONE
is_download: false
type: NONE
linear_start_addr: 0x80a5000
physical_start_addr: 0x80a5000
partition_size: 0x100000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS17
partition_name: tee1
file_name: tz.img
is_download: true
type: NORMAL_ROM
linear_start_addr: 0x81a5000
physical_start_addr: 0x81a5000
partition_size: 0x500000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS18
partition_name: tee2
file_name: tz.img
is_download: true
type: NORMAL_ROM
linear_start_addr: 0x86a5000
physical_start_addr: 0x86a5000
partition_size: 0x500000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS19
partition_name: kb
file_name: NONE
is_download: false
type: NONE
linear_start_addr: 0x8ba5000
physical_start_addr: 0x8ba5000
partition_size: 0x200000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS20
partition_name: dkb
file_name: NONE
is_download: false
type: NONE
linear_start_addr: 0x8da5000
physical_start_addr: 0x8da5000
partition_size: 0x200000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS21
partition_name: metadata
file_name: NONE
is_download: true
type: NORMAL_ROM
linear_start_addr: 0x8fa5000
physical_start_addr: 0x8fa5000
partition_size: 0x2000000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS22
partition_name: flashinfo
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0xafa5000
physical_start_addr: 0xafa5000
partition_size: 0x1000000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: false
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS23
partition_name: ADF
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0xbfa5000
physical_start_addr: 0xbfa5000
partition_size: 0x2000000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: false
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS24
partition_name: APD
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0xdfa5000
physical_start_addr: 0xdfa5000
partition_size: 0x6400000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: false
is_reserved: false
operation_type: INVISIBLE
reserve: 0x00

- partition_index: SYS25
partition_name: cache
file_name: cache.img
is_download: true
type: EXT4_IMG
linear_start_addr: 0x143a5000
physical_start_addr: 0x143a5000
partition_size: 0xC800000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS26
partition_name: system
file_name: system.img
is_download: true
type: EXT4_IMG
linear_start_addr: 0x20ba5000
physical_start_addr: 0x20ba5000
partition_size: 0xdfc00000
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS27
partition_name: userdata
file_name: userdata.img
is_download: true
type: EXT4_IMG
linear_start_addr: 0x1007a5000
physical_start_addr: 0x1007a5000
partition_size: 0x2aac56e00
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: true
is_reserved: false
operation_type: UPDATE
reserve: 0x00

- partition_index: SYS28
partition_name: sgpt
file_name: NONE
is_download: false
type: NORMAL_ROM
linear_start_addr: 0xFFFF0004
physical_start_addr: 0xFFFF0004
partition_size: 0x4200
region: EMMC_USER
storage: HW_STORAGE_EMMC
boundary_check: false
is_reserved: true
operation_type: RESERVED
reserve: 0x00