Centaurs are great, I likely won't any too soon but it's certainly possible, as are pregnancy mechanics. I think with pregnancy I'll be cautious though since not everyone's going to like that, it'd have to be something you'd only get if you go looking for it.
Once I finish the current girls I might add some sort of aquatic girl, a flying girl, that sort of thing. I want to diversify the cast much more than just the simple kemonomimi girls I have now.