My cynical nature wishes to see a antagonist that succeeds in changing their society in a realistic,surgical,profound and lasting way who doesn't look obviously evil and is not disposed to overconfidence, but possible damages to the general perception to the TV show would likely be profound and probably deprecating to it's success , and thus, an implementation of this would be unlikely (1% chance per major antagonist EX Nightmare moon, discord, queen chrysalis).
I figure that if such a antagonist were to be implemented, then the series will depart from it's roots cartoony antics and shift toward the quixotic combination of humor and cynicism.