I wouldn't actually mind some form of crossover of the
Bangaa from FFXII, assuming these are what you were talking about...

As for story reasoning, well, we have had crossovers from FFXIV and DQX I believe, its not entirely impossible for them to come up with some story to explain it, I mean, what if they said that a bunch of Bangaa came through a Void like monsters in VW or something to that extent? I think SE could make it work, the only question is is it viable and is it worth dev time and the answer is simply no, since the 5 races as they are now are hardly different from one another outside of aesthetics, especially with how high our stats are now that the gaps between most things besides HP are easily overlooked in the long run.
Besides that it would literally mean them redoing every piece of armor in the game with a .dat that would fit the new race, in this case, Bangaa, and they are very different than our current races with the most similar being Galka due to the large tail. I mean, I really do like the idea in theory, but it just wouldn't be good for the game with how much work would be involved and how little a difference it would make in the long run.