I seriously doubt SE will ever bother with the expense of making a third FF MMO, given they're basically stretched running two simultaneously already, and both are still making money for them (XIV especially so). MMOs are no longer the 'in' thing in gaming and given the current uncertainty in the world at the moment, it's unlikely they're going to take another gamble on a MMO, especially with so many failing (this is why SE has lately been releasing a lot of mobile social games, as that is where the big money is right now).

Of course, stranger things have happened though....