I'm going to try this on a Xperia E3. Things i'll try:
- set a RAID flag on partition /dev/block/mmcblk0p24 (/data) to work together with /dev/block/mmcblk1p2 (/sd-ext), also with raid flag;
- properly setup fstab to do the magic;
- compile kernel with raid support.
Some things more ,when I realize it, will be needed.
I apreciate anyone who want to help.
I'm jpzex on XDA-Developers.