Personally, I'd love to see more mane and 'hair' options, preferably with better looking meshes.
The ability to play more than two kinds of species would also be neat.
Being able to layer markings, probably up to three to five different ones would make me happy.
Boosting the number of items you can wear to ten would allow far more customization of characters.
Finally, would love to see some of the old maps everyone talks about that I missed out on brought back.
That said, if I ever sharpened my abilities making mesh and textures, I'd happily donate resources to Feral Heart for free.
That's a ways off, though.