At what point do we draw the line at letting them "try something new" against a current legal agreement?
I think we can all agree that the LENDERS would like to try new things too - so can we just arbitrarily change the agreements and do so? Why can't I just ignore the TOS and contact the lates myself? If they can change the rules willy nilly, why can't we? Because they are the upper hand. We are the peons.
It's a valid question. I don't think there is a correct answer, but I think your example isn't the line either. Prosper is attempting to work outside the legal agreement with the interests of all lenders involved and with (one hopes) due consideration to the legal ramifications of doing so to itself, the lenders and the borrowers.
If you (hypothetically) decide to waive some of the contract clauses and attempt to contact the borrower, there is no similar assurance that you have in mind the requirements of any laws in doing so, have the interests of PMI or the other lenders in mind.
However, if you do contact the borrower, I would speculate that Prosper would do very little except abrogate your access to their site and whatever else is necessary to insulate themselves and other lenders from legal issues created by your doing so.
So, go ahead. Give Prosper email notice that you intend to alter the terms of your lender's agreement with them and go ahead to contact some of your late borrowers. Let us know how that works out for you. I'm sure if that you report success, more lenders will follow your pioneering effort.