there are a few forums dedicated to AT technology(AT haven, AT Project 3...) and blueprints are being improved all the time. its only a matter of time before these become actual things, really. the problem is in getting motors that are compact, powerful, and efficient. seeing as increasing one of these will decrease another naturally, you'll have to find an acceptable balance between power and size. this not considering cost, of course. more expensive motors should perform better, but you can't make it super expensive either. more trade-offs!
also, never fall for the "power the skates with tiny wind turbines", or the "generators in the motors" tricks. things like this are cool, but way far out there, and will only inhibit progress. the first rule of engineering is to keep it simple!