The thing is, there has been a bit of a paradigm shift in game design since FFXI was released. Thanks to streaming and Youtube, there are as many people watching games as playing them. If you want a game to really take off now, it needs to be entertaining to sit and watch somebody else play, and FFXI is... well, not that. If you don't play FFXI, you're not going to watch someone else play it.

FFXIV is bigger and flashier, more going on on-screen to catch a viewer's eye, and it tries to be prettier with its glamours and its modern graphics. Raids are big, with the zoomed out camera so you can see the arena - because they paid for the whole room, they're using the whole room. It's much more streamable.

I think they would need to cater to that a little to make an FFXI remake that wouldn't just be needlessly spending money on an existing audience. I'm not sure how they could without changing the character of the game, maybe make animations more dynamic, or fix the "you cannot see the enemy" problem so fights can move around a bit more? Maybe give a "cinematic" camera mode players can choose to use, which gives that big scaled-out view of a fight, maybe give more visual telegraphing of major TP moves when a monster is supposed to be readying them? (Maybe host a server or two outside Japan so non-Japanese players can get to see monsters readying their TP moves before the damage from them is applied, as seems to be intended gameplay?)

And of course, in terms of just regular gameplay... nobody can say quests couldn't be better. I don't need every quest to tell me exactly what coordinates of what zone I need to visit like Seekers of Adoulin tended to do, but maybe when a quest has six steps that need to be completed in order, the quest log could tell me which step I most recently completed?

What FFXI really needs, though, is a tutorial. When I started playing, I was level grinding for probably two hours before I realized I started with equipment, and it wasn't equipped by default (on black mage! That was painful.) Just the basic controls are unintuitive enough that I've had people I tried to introduce to the game give up ten minutes in because they couldn't figure out how any of it even worked. First character on an SE account should get dropped into a tutorial zone to learn the basics of the game before bring dropped into a world that expects players to know everything and tries to punish ignorance.