Although they could make a new MMORPG, Yoshi-P probably wouldn't be able to commit their whole time to it like they can't FF16. SE has also tried to make other ones I think? Like most of their other games they probably failed.

Graphics being good isn't enough. The game would have to actually be good. Games like New World proved that those sort of graphics need something good behind it or it won't work.

I also just think it wouldn't be realistic to work on two competing MMORPGs at once. People would infer that Yoshi-P cares about one or the other more and go to that one. It would either have to be made by someone else (different SE unit) or in a world where Yoshi-P has stopped working on FFXIV.