Could checking, not only the reputation of the person in question, but also the reputation and trading history of the other identities help? AI will probably be useful in the decision making process too.

Also, I would expect that for _significant_ amounts, one would require some sort of id, address verification etc?

bitcoin

blend: a p2p borrowing and lending protocol

One problem that comes to mind is how to prevent an evil actor to create many identities and repeatedly lend himself to build up reputation, before "spending" it in ripping someone off.

On the other hand, one positive idea that came to mind is: if a single loans could be served by many lenders, that helps the lender side of the market distribute risk. Like, if there was some coordinating mechanism in the protocol that makes it trivial for a loan to be funded by many lenders, maybe even pretty much the standard thing. I feel this leads to interesting options. 

This is the kind of cool stuff that we can do and traditional finance can't because of all the friction they face.