Wow, I came up with this idea last year and thought about implementing something similar.
The idea is awesome when you're dealing with commissioners you don't know or trust as the interactions can happen directly between you and the "bank" (I called it an escrow account in my mock-up). The "bank" just simply puts the funds into a 3 month CD or something that is interest bearing and makes money on the interest.
It's a smart idea (that's why I came up with it
) but the trick is getting people to actually use it. The idea is best to create and show as a proof of concept and then sell to someone like Yahoo for a tidy profit.