Status update: got a working kernel based on 2.6.30 linux-omap and android - will probably have to set up git somewhere at some point because trying to describe all the cherry-picks, merges, and hacks I had to do to get it booting an Android userland init is going to be hard otherwise.

Some notes for future porters though:
Android userspaces need ASHMEM. They won't even start to do anything without it.
GCC 4.4.0 and 4.3.1 won't build a booting kernel easily. Using 4.2.1 to build the kernel seems a lot more stable.
linux-omap HEAD doesn't init the framebuffer - I think someone accidentally refactored it out when they moved from n800-board-xxx.c to n8x0-board.c and tried to put init in individual drivers. You have to use something from around 2.6.30 (my git will have the specific commit), before the n8x0-board refactor.
2.6.30 has some Android code merged to mainline that works, but not everything (notably ADB Gadget, GPIO Input, its dependencies such as switch and block_wake and ASHMEM will need to be cherry-picked and frontported - some USB name stuff was redone so ADB Gadget needs some love).

Now I'm just having much more straightforward rootfs mount / init script issues.

My new kernel has WiFi drivers built-in (still need firmware, obviously+sadly), and support for watchdog etc. was put into linux-omap mainline. Sound theoretically works too but I haven't even thought about testing it yet. So we'll have a lot less deps on a Nokia initrd, but they're still there (firmwares now, mostly).