Interesting thought . . .
My gs3 (I535) Is rooted running CleanRom 6R2,TWRP 220.127.116.11, & LeanKernel 3.0, & after several roms/upgrades, I finally have it the way I like it. Love it, in fact. Just for giggles, If I were interested in upgrading to the Gs4, & rooted /unlocked the bootloader, etc, Would it be possible to copy a recent recovery of my current Gs3 system & restore that backup to a rooted bootloader unlocked Gs4 & have it actually work - ?
Now, I realize that I would have to use the Gs4 radio & device specific software for the camera, etc . . . Just curious if such a transfer of a custom rom & system was possible . . .