It sounds like you already have a 26-inch-wheel bike, so grab a wheel and see if you can fit it in the UNO frame. You don't have to worry about brake reach 'cause you have discs, so all that matters is the tire clearing the top of the fork and rear bridge. I doubt it would clear a big knobby, but you might get lucky with a 1.5 city tire.

I'm not sure what you mean about swapping wheels, though. Once you have the Alfine installed on the Tern, it's not a quick job to move it to another bike.