It's not hard to model a character or to rig them if one's skilled enough (with enough reference photos, a friend and I can make models between a few hours or a couple of days). The annoying part is animating them.
To put a new species into FeralHeart, all that would need to really be done is to recycle code for the programming part. I mean, there's already flying because of wings, right? It'd be easy as pie to put a dragon or bird in XD
It's the animating/importing part that would take time, as well as texturing and other things.
But either way, even if it took a long time, things that take time seem to be better. If it was really fast then it wouldn't have a good quality, LOL.
I don't really agree with other animals on the game, as it simply doesn't seem to fit very well with FeralHeart as a basic whole, so it's not the amount of work that bothers me personally, but trying to make them fit both in the game society and artistically.
I mean, really, what would a dragon character honestly look like with the art style of FH, anyway? That would always be my first question, because too realistic/too cartoony would clash with the other models.