I even tried to restore the stock ROM with fastboot, flash the latest version of TWRP
There's really nothing to do, my xoom is ruined !!!???
I feel your pain, yours is typical of the story that prevents me from upgrading my Xoom from EOS3.
I can only suggest you try to restore it to factory state using fastboot.
The poster below you has already done this with success http://forum.xda-developers.com/moto...illed-t2852314
There is also this link http://forum.xda-developers.com/show....php?t=2635282 that may help as well.
You may have already tried those methods, if so then I don't what else to suggest.
What version of TWRP? I found that using 220.127.116.11 was formatting my /system, /cache, /data to f2fs instead of ext4.
Make sure that those 3 are formatted for ext4 when installing your ROMs. I was able to BigPart and un-do BigPart with TWRP 18.104.22.168 but struggled when attempting to use 22.214.171.124
Good luck, your tablet should definitely be fixable