I don't think Square has the budget for a new MMO, and even if it did, they tend to have unrealistic expectations with their titles, if their response to FFXVI's sales are any indication. We're riding with FFXIV and FFXI for the foreseeable future. I don't know how the game works under the hood exactly, but I imagine they have the capability to try new things if they really wanted to. It's a matter of man-hours and not wanting to mess with the Shadowbringers formula that made them successful, I imagine.