For good reasons, +nan.0 is not = to any other number, including itself. However, eqv? is about "sameness" rather than "equality". I propose that we add two clauses to the definition of eqv?, one saying that if both arguments are +nan.0, eqv? must return #t, and if one argument is +nan.0 and the other is not, eqv? must return #f.
All of my usual test Schemes already behave this way, with these exceptions: