From the FAQ on
http://www.ibrinfo.org/faq.vp.html#takenaway
(Taken with grain of salt)
"IBR and Public Service Loan Forgiveness were passed into law through the College Cost Reduction and Access Act of 2007, and any major changes to these programs would require new legislation to be passed by Congress and signed by the president. This is highly unlikely to occur in the foreseeable future, and we recommend that borrowers proceed with confidence."
Unfortunately, nobody can say for sure. But, what do you mean by "whether or not I want to spend an extra 90k or not for med school" ?
Are you saying (1) you have $90k available and are trying to decide whether or not to use it for med school? Or are you saying (2) you're trying to decide whether or not to attend a med school that costs $90k more than another? Or (3) you're trying to decide whether to go to med school or not, based on the cost?
(1) If you have the $90k sitting around, put it in a secure investment like a 7 year bond or CD or something. Go to med school and then do IBR during residency at a non-profit hospital (there are some that aren't). If PSLF is still in effect for docs when you're done, keep going with IBR at non-profit.
If at that point the @#&%@'s in Washington have taken PSLF away from us, throw your $90k+interest earned at your loan principal and then finish it off in a couple more years.
(2) If you like the cheaper school, go there. Work your butt off, get involved in clubs, network, get good LOR's, etc... You will get the residency you want regardless of where you go.
(3) First decide whether you want to be a doctor or not, regardless of money. THEN worry about the finances of it.