The idea of these becoming common on the slopes scares the crap out of me. I've won every collision that I've had with bikers at the skatepark but something tells me that wouldn't be true on the hill getting hit from behind. I wonder if those things have the same control problem that ski-blades do?
One of my ski buds, tweaked his knee last year and rode a fully suspended ski bike with a break. It looked fun and more of a green run kind of thing and the hill had more natural hits, so no need to take into the park...the hill would not let him take it on blacks and double blacks.