... as a person of the female persuasion who actually used to collect what most would consider to be furry porn (art prints by my favorite artist), I don't think there's a line that's being crossed here as long as it's tastefully done and not blatant. It's 'elegant' and not, well, crass? so I don't think you have anything to worry about. Hell, I didn't even notice the nipples until I looked more closely at the strip, and this is pretty tame compared to most.
Take Friday's strip vs something like CnC (Cats and Cameras) where the obvious sexual situations are all written in to appeal to guys, written by a guy, for the express purpose of adding to the spank bank, and there's a really big difference.
Not that these strips are necessarily necessary to push a relationship forward, but it IS kind of nice to see that they're intimate and maybe having some teasing at a characters expense later