[Android Software/Hacking General [Developers Only]] IzaacJ:
Sadly, no success.

Some info from the recovery log:

Section about the boot partition

/boot | /dev/bootimg | Size: 16MB
Flags: Can_Be_Backed_Up IsPresent Can_Flash_Img
Primary_Block_Device: /dev/bootimg
Display_Name: Boot/Kernel [boot]
Storage_Name: boot
Backup_Path: /boot
Backup_Name: boot
Backup_Display_Name: Boot/Kernel [boot]
Storage_Path: /boot
Current_File_System: emmc
Fstab_File_System: emmc
Backup_Method: dd

And the installation:

Installing zip file '/external_sd/superuser-r273.zip'
Checking for MD5 file...
Skipping MD5 check: no MD5 file found
I:Zip does not contain SELinux file_contexts file in its root.
I:Legacy property environment initialized.
+ fd=27
+ [ ! -L /proc/self/fd/27 ]
+ zip=/external_sd/superuser-r273.zip
+ ui_print Installing seSuperuser...
+ echo ui_print Installing seSuperuser...
Installing seSuperuser...+ rm -Rf /tmp/superuser
+ mkdir -p /tmp/superuser
+ unzip -o /external_sd/superuser-r273.zip -d /tmp/superuser/
Archive: /external_sd/superuser-r273.zip
creating: scripts/
inflating: scripts/bootimg.sh
inflating: scripts/.gitignore
inflating: scripts/kernel_subkey.vbprivk
creating: scripts/su/
inflating: scripts/su/changes.sh
inflating: scripts/su/su-communication.sh
inflating: scripts/su/rights.sh
inflating: scripts/README.md
inflating: scripts/kernel_data_key.vbprivk
inflating: scripts/kernel_data_key.vbpubk
inflating: scripts/gitversion
creating: scripts/keystore_tools/
inflating: scripts/keystore_tools/README
inflating: scripts/keystore_tools/make_key
inflating: scripts/keystore_tools/BootKeystoreSigner.jar
inflating: scripts/keystore_tools/BootSignature.jar
inflating: scripts/kernel_subkey.vbpubk
creating: scripts/bin/
inflating: scripts/bin/su-x86
inflating: scripts/bin/hidesu
inflating: scripts/bin/sepolicy-inject
inflating: scripts/bin/sepolicy-inject-v2
inflating: scripts/bin/futility-arm
inflating: scripts/bin/bootimg-repack
inflating: scripts/bin/su-arm
inflating: scripts/bin/strip-cpio
inflating: scripts/bin/bootimg-extract
inflating: config.txt
creating: META-INF/
creating: META-INF/com/
creating: META-INF/com/google/
creating: META-INF/com/google/android/
inflating: META-INF/com/google/android/updater-script
inflating: META-INF/com/google/android/update-binary
+ cat /tmp/superuser/config.txt
+ modes=eng verity crypt hidesu
+ cd /tmp/superuser/scripts/su/
+ fstab=/etc/recovery.fstab
+ [ ! -f /etc/recovery.fstab ]
+ grep -E \b/boot\b /etc/recovery.fstab
+ grep -oE /dev/[a-zA-Z0-9_./-]*
+ bootimg=/dev/bootimg
+ [ -z /dev/bootimg ]
+ ui_print seSuperuser: Found bootimg @ /dev/bootimg
+ echo ui_print seSuperuser: Found bootimg @ /dev/bootimg
seSuperuser: Found bootimg @ /dev/bootimg+ sh -x ../bootimg.sh /dev/bootimg eng verity crypt hidesu
+ export TMPDIR=/tmp/
+ which mktemp
/sbin/mktemp
+ [ 5 == 0 ]
+ set -e
+ [ -f eng ]
+ scr=/tmp/superuser/scripts/su/changes.sh
+ trap cleanup EXIT
+ readlink -f ../bootimg.sh
+ dirname /tmp/superuser/scripts/bootimg.sh
+ scriptdir=/tmp/superuser/scripts
+ chmod 0755 /tmp/superuser/scripts/bin/sepolicy-inject
+ chmod 0755 /tmp/superuser/scripts/bin/sepolicy-inject-v2
+ chmod 0755 /tmp/superuser/scripts/bin/bootimg-repack
+ chmod 0755 /tmp/superuser/scripts/bin/bootimg-extract
+ chmod 0755 /tmp/superuser/scripts/bin/strip-cpio
+ [[ toto2 =~ toto ]]
sh: =~: unknown operand
+ r_file_perms=getattr open read ioctl lock
+ x_file_perms=getattr execute execute_no_trans
+ rx_file_perms=getattr open read ioctl lock getattr execute execute_no_trans
+ w_file_perms=open append write
+ rw_file_perms=getattr open read ioctl lock open append write
+ rwx_file_perms=getattr open read ioctl lock getattr execute execute_no_trans
+ rw_socket_perms=ioctl read getattr write setattr lock append bind connect getopt setopt shutdown
+ create_socket_perms=create ioctl read getattr write setattr lock append bind connect getopt setopt shutdown
+ rw_stream_socket_perms=ioctl read getattr write setattr lock append bind connect getopt setopt shutdown listen accept
+ create_stream_socket_perms=create ioctl read getattr write setattr lock append bind connect getopt setopt shutdown listen accept
+ r_dir_perms=open getattr read search ioctl
+ w_dir_perms=open search write add_name remove_name
+ ra_dir_perms=open getattr read search ioctl add name write
+ rw_dir_perms=open getattr read search ioctl open search write add_name remove_name
+ create_dir_perms=create reparent rename rmdir setattr open getattr read search ioctl open search write add_name remove_name
+ startBootImgEdit /dev/bootimg
+ readlink -f /dev/bootimg
+ f=/dev/bootimg
+ homedir=/tmp/superuser/scripts/su
+ mktemp -d
+ bootimg_extract=/tmp/tmp.XjU4My
+ cd /tmp/tmp.XjU4My
+ /tmp/superuser/scripts/bin/bootimg-extract /dev/bootimg
Segmentation fault
+ cleanup
+ rm -Rf /tmp/tmp.XjU4My
Updater process ended with ERROR: 139
I:Legacy property environment disabled.
Error installing zip file '/external_sd/superuser-r273.zip'