If it's possible to compile a "clean" N900 kernel with working features you'd want in Android, the Android 2.0 userspace is actually very straightforward to build. I did it on a whim last night for N810, and besides nonworking N810 features / extra loaders / all the crap that comes with closed/proprietary kernel extensions (loading wifi firmware, DSP, and so on) it's working quite okay. Depending on the state of the N900 kernel merging the Android extensions could be a quick merge and compile or a little ordeal, but shouldn't be too complex as they don't interact too much with other parts of the kernel (they mostly extend the kernel to monitor memory, kill tasks, and provide logging services, rather than hitting any hardware or mangling any drivers or kernel structs).

Making Android work with a new baseband/radio is something a little more tricky, again depending on the N900 kernel (which I know very little about). The people who ported Android to the HTC Vogue did it, though (they even reverse-engineered the baseband driver, although they didn't have to do the hard parts like bringup since Windows Mobile did it for them).

Overall there is no reason this is not possible given a working, clean, user-buildable N900 kernel which I have yet to see.

Android 2.0 will run fine regardless of the LCD's actual color depth - what it needs is a 16-bit RGB565 mappable framebuffer, which almost all framebuffer drivers provide (including the N8xx's and presumably the N900's).

All of this shady leaked stuff and HTC code is unnecessary - the Android 2.0 source is freely available from Google themselves and compiles up just fine. The only time shady (legally and functionally) dumps are necessary is if you want the By Google apps, which isn't really relevant to "will Android run on the N900" anyway.