... As for "merely lending", there is a quantifiable gift involved, the free use of money which would otherwise attract x% interest, as well as the mathematical certainty (on a very large loan portfolio) of capital loss at whatever percentage rate per year.
While that may be perceived as an emotional donation, the IRS (in the US) has never considered "opportunity loss" a tax deductible donation. Probably on the theory you would have to declare the income lost first as income before you could take a deduction for giving it away. Essentially a wash.
To be truly efficient in allowing donors to direct their donated loan portfolios, Kiva has to be directly involved so that the accounts are set up appropriately. On another thread there has been a discussion of sub-accounts to give to children etc, which would get credit infusions from outside and would not allow withdrawals. Mechanically these would operate the same as donor directed charitable accounts, so now we have two constituencies who can request this modification from Kiva.
However, since it takes resources and a commitment of manpower to set up this charitable purpose entity, I think it will need to be someone or something other than Kiva to take the lead here. They just have too much on their plate right now. And it least for now they are getting about the same benefit with the way things are right now.