[simonsez]

Right, so all of those work now through the existing financial system, but they take a long time to clear (I believe ACH is several days).

I imagine a startup (would it have to be a bank? I'm not sure) could build something where the transfer is semi-instantaneous and disperse the risk among it's other customers somehow in a more equitable manner (perhaps charging a fee?). It might, of course, be difficult to compete against the credit card, which seems free to most consumers (but is subsidized by the merchants and those borrowers who don't pay in full)