Would you even have to make an epic plot? Some good writing and game mechanics could carry a nothing game a long way. It may have to do with the music I'm listening to, but the idea occurs to me that with the fans of this game, you probably don't have to go on some epic quest. You could have a Stardew Valley experience within the FFIX universe and I bet most fans would be more than happy. As long as there's tons to do, lots of characters to interact with, and a sense of time progression so you don't feel like you're just playing a long minigame

Unfortunately I don't think Square Enix has the chops for that...kind... -well, actually, now that I think about it, Dragon Quest Builders delivered just such an experience. You'd have to put a lot more work into the world and characters and art style for a FFIX game in that vein, but I guess they could theoretically do something like that. Final Fantasy IX The Sims