So far I only see tails and wings as "extra" parts, and will probably be it for a number of years.
Personally though I would love to be able to have choices like like four legs, both in "feral" and taur form. Different kinds of insects (6-8 legs, or possibly even the hundreds that some centipedes appears to have), again both in "feral" and taur/drider form but also with having multiple pairs of arms instead of legs (like 4 arms and 4 legs). Non-legged bodies like snakes and nagas, or even mechanical tracks/wheels.
On the flip side I would also like the option for no legs and/or arms. Heck even just a simple geometric shape could be useful, like a super advanced robot that is contained inside a perfect sphere.
Realistically speaking though I don't see them going beyond quadruped options (and possibly geometric shapes), if we get any such options at all. The amount of work in getting the skeleton, all the morph points, animations and costume options right is just too much work in the long for, probably, not that big of a return.