I think that of all the collections of races Final Fantasy has had, Ivalicians are the best assortment, and I'd take Viera over Miqo'te any day, but I would highly doubt that they'd bring races from other 'worlds' to Eorzea. More likely, it would be an Eorzean imitation of some other popular Final Fantasy race, and I can't think of one that would be begging to be added... maybe with the idea of an Ishgard expansion a variation of the Gria would be interesting, but I can't really think of anything else...