Ah!!! I think I have an idea... Partition the sdcard with an ext4 partition to allow symlinks (a big one at that... Least a few gbs)... Move your current roms partitions to it... (/cache, /data, /system, kernel)... Flash another ROM... Write a script that recursively hides all files and folders on the newly installed rom by adding a "." In front of them... Then recursively symlink every file of the original ROM that's located on the sdcard into the current partitions (again that's /cache, /system, and /data)... Swap kernels through normal methods within the script... Bam! Dual boot!!! And of course to switch ROMs you'd have to create a script that reverses the process... By doing it this way there is 100% no moving around files... So it wouldn't take very long to do... Only renaming and symlinking... However... No USB mounting through the ROM on the sdcard... Since its located on the sdcard :banghead::banghead::banghead: also I'd imagine that you'd need a fast sdcard... Very fast... Also this assumes that by adding a "." In front of file names on the partitions that it prevents them from being read as if in normal startup... Maybe it'll work... Maybe it won't... Just brainstorming *shrugs shoulders*