IETF RFC: Ask question to the author
An IETF RFC may often be thought of as a certain peculiar form of scientific publication: they are frequently cited as such, feed research programs, and can indeed significantly count toward the evaluation of one's research career.  Certainly that has been the way of it for people who I have known who have authored RFCs or otherwise participated in the IETF.

As such, contacting the author of an IETF RFC is not particularly different than contacting the author of a scientific paper: make sure you do your homework first (as it sounds like you've done), so that you don't embarrass yourself or waste the authors' time, and then feel free to contact them.  Their contact information is there for a reason.