It seems more likely that if we get any new races they wouldn't come in till we start exploring the New World. The only race that hails from there and not Eorzea right now are the Mamool Ja to my understanding, and would be the perfect time to introduce any sort of new playable race including Viera.

But this would also be quite a few expansion out, not until at best 6.0. More likely 7.0. Which given we got Au Ra still puts us ahead of XI in that aspect.