This is a bootable device tree for the Kobo Touch. I managed to make it boot but then I got bored, so here it is for you to play.
It is definitely incomplete and probably partially incorrect, but it boots and it is able to mount a rootfs from either SD card.
Interrupts are all commented-out since I haven't fully figured them out. The values I specified are incorrect and enabling them causes the kernel to freeze, most likely because I'm incorrectly wiring them to floating GPIOs causing an interrupt storm which saturates the CPU time.
Note that mainline Linux has no driver for the touch screen and e-paper display, so while the system will boot you cannot display anything.