Well it does not work in my case. I have extracted rootfs.jffs2 again, mounted it with -o ro switch and cloned the filesystem, but it does not work It hangs in exactly the same place ... with the message booting from immc2 (mmblk0p2 ext2) and then reboots after a while (without the usual dsme led flashes). Will keep on investigating...

UPDATE: I have tried to check what is going wrong by starting usb networking (enabling persistent connection while booting in the process) but the moment I select to boot from mmc2, usb net connection is severed.