I would absolutely love to try a ski-bike, especially with a dirt bike like cockpit, bonus points if you get a free kazoo for 2-stroke engine noises. The Snow-Moto concept looks interesting as well but you can't do seated, foot-out MX style turns. Maybe a cross between the two is the sweet spot.
I've seen a few people riding one-wheels on the easier MTB trails in town and I think it's great. It's actually quite impressive to see.