I'll pretty much say the same thing from another thread with the same topic. Anyway, It doesn't even have to be a Final Fantasy MMO.

I want a game with a living, breathing, seamless and open world that is actually relevant and gives you a sense of adventure. I do not mind instanced content but FFXIV focuses on it too much, which leaves the open world abandoned and incredibly boring in design.
Action combat with weight and button efficiency. Personally I'm tired of tab-targetting combat and SE could go with something different if they're going to develop a new FF MMO.
Jobs with options to customize, even if it's cosmetic or affects gameplay very little. It's more fun to play something when it's tailored it to your preferences.
Encounters that feel organic and not scripted. More on enemy movement predictions with no lazily highlighted enemy attacks that just look ugly. Crowd control being more relevant to help you with fights.
Meaningful stats that actually affect gameplay. Something like what Monster Hunter has where you can enhance or add certain abilities or conditions onto your character depending on your armor's/decoration's skills.
Better character customization overall.
More expansive and better inventory system.
And most of all, a flexible and powerful engine to run the game with. I'm tired of the amount of parroting the FFXIV dev team has done because of the awful engine the game has.