wow that is really cool!! Thank you!! I would also like to announce the next steps. I currently failed to manage to run a successful compile for android. But since time is currently limited I started digging into rockbox again.
-> Kernel 2.6.24 successfully compiled and is now fully bug free also with ext2
-> I will do a quick and dirty messing around: I will format my sd card to ext2 and mount it at bootup which contains the entire cramfs. I will put sdl into the cramfs and bind my mmc to / root and try to start up rockbox. the cool thing is. if it can't mount the sd card everything is back to normal (so take it out and everything is fine). Also I wouldnt need to flash my device anymore since I can work on the sd card instead.