I think this is an excellent area of exploration. However i have a few reservations, how will you compensate for loans that default ? If you don't charge anything for lending out money your net result will be negative.

I myself have studied both Islam, Judaism, and Christianity, and i do know all of the 3 have historically played with the devils advocate... The Christians outsourced usury to Jews when the pope demanded end of interest, and i do know that todays modern "Islamic Banks" (are not Islamic at all) those banks "resell properties at a premium for longerterm periodic payments" making it equal to usury (but on paper they can say "hey we're 100% Sharia we don't charge interest!").

The way i see it, the bank together with potential investors/bank could do as you say "joint venture" with a client who requests a loan, making it a "equity investment" which should be 100% Bible/Koran compatible if the investment appreciates in value investors, the client and the bank profit, if it declines all the 3 parties share the loss (this also seems as most ethical form of banking). Now, this makes sense. But it gets complicated, you plan to offer this service to anyone ? (some anonymous person can request an investment in a project, commerical or consumer) ?

I think this seems like a very risky business. How will you deal with reducing fraud/abuse ?