The Switch 2 is a fairly weak platform, and most mmorpgs (including ffxiv probably) would never work well on it. However it is a massive platform, and given its size any mmorpg on it would have a huge advantage.
XI was made for PS2 and controller and still has fairly low requirements to run (the point you can run 6 instances or more on a very humble computer), and I'm sure it would not require a massive a amount of work to port over to it.
Is a version of FFXI for the Switch 2 a possibility? Is it something YoshiP would consider investing in?