I don't know much about Tahoe-LAFS, but if there's no built-in incentive to provide storage, I'm guessing there's also no built in verification that you're actually storing what you say you are.

If there's an incentive system for providing p2p storage (which is something I really hope to see), there needs to be a very robust verification scheme, otherwise people will fake it for free money. To me this seems an extremely challenging problem, though probably solvable (I did spend some time thinking of some possible solutions).

Whether we use Bitcoin or OT or both or neither for payments is trivial in comparison.