But I wonder if universities should offer some sort of deferred payment (5 years after graduation for instance) to students instead (not a 3rd party loan). If you go to Stanford you are pretty much guaranteed a stable income when you graduate. Yes ,granted, a lot of alumni do donate without feeling the necessity to do so, but having such an option will help universities, perhaps more for those with smaller endowments "recover" some of the cost.
Universities could always make exceptions some time down the line on a case by case basis, depending on student's current income which will vary violently even for top universities, with some students deciding to work for a non-profit while others choosing a more lucrative job, just like income tax works.
Again, I am really not sure, just throwing it out there.