If you are looking for one, here are some tips:
- hw keyboard
- open source drivers or at least linux-compatible blobs (binary android ones are useless)

When the DragonBox Pyra comes out, its variant with modem might be a nice device to use Maemo on. But, according to Wikipedia, it will ship with Debian... So maybe porting whole Maemo won't make so much sense - porting Hildon, maybe few libs and recompiling apps will be the way to go.