That unlimited detail thing interests me, i have asked if they are going to make a Linux version, but the SDK is estimated to be out in around 14 months... =(
It is the newest 3D system to date, though, and the best. I hope it can take normal poly-models when its done.
If that was what was going to drive it, we would be talking 3D quality as good as Twilight Princess and even better. I can soon show what i have made so far of the Hyrule Field for the game, it will surely be the center of adventures and packed with things to do. =D (I am thinking about giving the possibility of boat-trips that you control yourself.)

Some effort was being made to port Ogre3D to Maemo. That may be your best bet for a powerful 3D engine. I'd suggest you worry about reducing detail after you get to the point of a functional renderer, when you can actually see what the performance is like with everything else going on.

First lesson of coding: functionality first, THEN optimize.