I'm willing to see medusae as more "mythological human-based creature" than reptile. The only thing that makes them snaky is their hair, which, along with their petrifying appearance, could as easily be the result of their divine curse. As for nagas: No, I don't think they do have breasts. None of the ones I've seen in D&D art do, anyway.
Anyway, point is that there are already *plenty* of human-like races with sufficiently plausible anatomies to get the cheesecake fans salivating. I'd rather see something like a dragonborn look demonstrably reptilian, maybe even more T-Rex like (minus the tiny arms).