[General Questions and Answers] Machine Improvement:
Over the course of my 4-month crash course trying to make some sense of Android hardware, I've been pursuing an independent line of research. The information on the following forums may prove useful:

"forum.hovatek.com/thread-526.html"

"forum.hovatek.com/thread-440.html"

"forum.hovatek.com/thread-13347.html"

"forum.hovatek.com/thread-12719.html"

What I found:

There are copies of a couple earlier Voyager models' scatter files with the same MT8127 chipset at ("xdaforums.com/general/general/stock-rom-twrp-root-oc-uv-rca-7-voyager-t3087075"). The MTK Droid Tools do not normally work with the RCT6873W42KC, but by replacing the default ADB folder in it with a newer version (1.0.32), the device showed up (minus its baseband data). While it did not allow me to generate a scatter file, it did show me the RCT6873W42KC's relevant scatter info. I am hoping someone with past experience in Android hardware finds this data useful.

So I proceeded to modify the earlier Voyager scatter to match the sector offsets and sizes to the data on the RCT6873W42KC. Be forewarned, however, that there were no MBR, EBR1, PROTECT_S, EBR2, or FRP records in the unmodified scatter, so I can't be sure their parameters are correct:

(from modified MT8127_Android_scatter.txt, copied from Notepad++)

############################################################################################################

#

# General Setting

#

############################################################################################################

- general: MTK_PLATFORM_CFG

info:

- config_version: V1.1.1

platform: MT8127

project: rct6873w42m

storage: NAND

boot_channel: NONE

block_size: 0x400000

############################################################################################################

#

# Layout Setting

#

############################################################################################################

- partition_index: SYS0

partition_name: PRELOADER

file_name: preloader_rct6873w42m.bin

is_download: true

type: SV5_BL_BIN

linear_start_addr: 0x0

physical_start_addr: 0x0

partition_size: 0x40000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: BOOTLOADERS

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS1

partition_name: MBR

file_name: mbr_rct6873w42m.bin

is_download: true

type: SV5_BL_BIN

linear_start_addr: 0x0

physical_start_addr: 0x0

partition_size: 0x80000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: BOOTLOADERS

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS2

partition_name: EBR1

file_name: ebr1_rct6873w42m.bin

is_download: true

type: SV5_BL_BIN

linear_start_addr: 0x80000

physical_start_addr: 0x80000

partition_size: 0x80000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: BOOTLOADERS

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS3

partition_name: PRO_INFO

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x100000

physical_start_addr: 0x100000

partition_size: 0x300000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: PROTECTED

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS4

partition_name: NVRAM

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x400000

physical_start_addr: 0x400000

partition_size: 0x500000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: PROTECTED

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS5

partition_name: PROTECT_F

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x900000

physical_start_addr: 0x900000

partition_size: 0xA00000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: PROTECTED

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS6

partition_name: PROTECT_S

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x1300000

physical_start_addr: 0x1300000

partition_size: 0xA00000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: PROTECTED

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS7

partition_name: SECCFG

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x1D00000

physical_start_addr: 0x1D00000

partition_size: 0x20000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: INVISIBLE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS8

partition_name: UBOOT

file_name: lk.bin

is_download: true

type: NORMAL_ROM

linear_start_addr: 0x1D20000

physical_start_addr: 0x1D20000

partition_size: 0x60000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS9

partition_name: BOOTIMG

file_name: boot.img

is_download: true

type: NORMAL_ROM

linear_start_addr: 0x1D80000

physical_start_addr: 0x1D80000

partition_size: 0x1000000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS10

partition_name: RECOVERY

file_name: recovery.img

is_download: true

type: NORMAL_ROM

linear_start_addr: 0x2D80000

physical_start_addr: 0x2D80000

partition_size: 0x1000000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS11

partition_name: SEC_RO

file_name: secro.img

is_download: true

type: NORMAL_ROM

linear_start_addr: 0x3d80000

physical_start_addr: 0x3d80000

partition_size: 0x600000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS12

partition_name: MISC

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x4380000

physical_start_addr: 0x4380000

partition_size: 0x80000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: INVISIBLE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS13

partition_name: LOGO

file_name: logo.bin

is_download: true

type: NORMAL_ROM

linear_start_addr: 0x4400000

physical_start_addr: 0x4400000

partition_size: 0x300000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS14

partition_name: EBR2

file_name: ebr2_rct6873w42m.bin

is_download: true

type: SV5_BL_BIN

linear_start_addr: 0x4700000

physical_start_addr: 0x4700000

partition_size: 0x80000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: BOOTLOADERS

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS15

partition_name: EXPDB

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x4780000

physical_start_addr: 0x4780000

partition_size: 0xa00000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: INVISIBLE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS16

partition_name: TEE1

file_name: tz.img

is_download: true

type: NORMAL_ROM

linear_start_addr: 0x5180000

physical_start_addr: 0x5180000

partition_size: 0x500000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS17

partition_name: TEE2

file_name: tz.img

is_download: true

type: NORMAL_ROM

linear_start_addr: 0x5680000

physical_start_addr: 0x5680000

partition_size: 0x500000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS18

partition_name: KB

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x5b80000

physical_start_addr: 0x5b80000

partition_size: 0x100000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: PROTECTED

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS19

partition_name: DKB

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x5c80000

physical_start_addr: 0x5c80000

partition_size: 0x100000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: PROTECTED

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS20

partition_name: FRP

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x5d80000

physical_start_addr: 0x5d80000

partition_size: 0x100000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: PROTECTED

d_type: LOW_PAGE

reserve: 0x00

- partition_index: SYS21

partition_name: ANDROID

file_name: system.img

is_download: true

type: UBI_IMG

linear_start_addr: 0x5e80000

physical_start_addr: 0x5e80000

partition_size: 0xa0000000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: FULL_PAGE

reserve: 0x00

- partition_index: SYS22

partition_name: CACHE

file_name: cache.img

is_download: true

type: UBI_IMG

linear_start_addr: 0xa5e80000

physical_start_addr: 0xa5e80000

partition_size: 0x10000000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: FULL_PAGE

reserve: 0x00

- partition_index: SYS23

partition_name: USRDATA

file_name: userdata.img

is_download: true

type: UBI_IMG

linear_start_addr: 0xb5e80000

physical_start_addr: 0xb5e80000

partition_size: 0x2e5c80000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: true

is_reserved: false

operation_type: UPDATE

d_type: FULL_PAGE

reserve: 0x00

- partition_index: SYS24

partition_name: BMTPOOL

file_name: NONE

is_download: false

type: NONE

linear_start_addr: 0x1500000

physical_start_addr: 0x1500000

partition_size: 0x1500000

region: NONE

storage: HW_STORAGE_NAND

boundary_check: false

is_reserved: true

operation_type: RESERVED

d_type: LOW_PAGE

reserve: 0x00

As implied above, I can't claim to be an expert, but I have a theory. While attempting a readback, running the flash tool as administrator, the progress bar stayed at 0%. I am attempting to figure out why, but one thing is clear: the device gives me no indications on whether it uses NAND or EMMC storage. Trying again, I replaced all mentions of "NAND" with "EMMC" and renamed the file to "MT8127_Android_scatter_EMMC.txt", with nearly the same result (no error message saying this device uses EMMC storage; be aware that there is a bug that causes the flash tool to falsely report NAND as EMMC, so I advise continuing to try both). Narrowing down the list of culprits, if anyone here already knows off the top of their heads how to put this particular model into META mode, that might be precisely what we need.

A final heads-up, I had already crashed my device once in an interrupted readback. If this happens to you, and it appears not to be turning on and your computer won't recognize it, plug your device into the charger for a few minutes and then put it into recovery mode.