There was a brief thread talking about "snap-in" pickup installation possibilities some months ago, I think. Fabulous idea, IMO, but unless manufacturers agreed on a standard mounting system, you'd end up with Beta vs. VHS -- or at best you'd be locked into using the BKP "FastFit Pickup Cradle" forever (which, actually, doesn't seem so bad :)).
Surely what prevents more players from buying more pickups is the hassle of installing them? It'd be so much more convenient to just buy new pups that you could slap in in moments (loosen up the strings at bit, I guess, and slide 'em under) rather than buying multiple guitars to load with multiple pickups. Then pickups would become basically like effects pedals: not so different in price and almost as easy to swap in and out of your rig.
Ah well. We can but hope for the future!