I've seen quite a few efforts like this, one bike even made entirely from springs (I think that was Colin Furze?). But the magnet idea is a good one - no friction means no wear. Although, it would eventually pick up bits of dirt with metallic fragments in, but if it had a dust seal surrounding it, might not be an issue. I think there was also the idea of putting opposing magnets in the road to power cars (a bit like an induction hob) but I guess that is many years off and possibly not even workable