I think Vivi is probably the most beloved character for sure and that would probably do the trick but if this is a full on remake it was likely expensive meaning they'll need to make it likely more mass market appealing than the OG it's why remakes have been so hit and miss some people want the complete original with a new coat of paint, some people want a reimagining, and others just want them to leave it alone.
Right, opinions are always split because no market is a monolith.
Of the three positions you're describing though, one of them isn't valid in my mind. That is the "leave it alone" position because regardless of what a remaster, re-imagining, or remake does, the original remains, so it
is left alone. Now having the opinion that the existing game is good enough
is a valid position, so I'm not calling that invalid. But because the original will be left alone regardless, it's invalid to use that as a reason against anything else.
As for the other two positions, those are both valid. In my mind, both types of remakes work and it comes down to some specific factors on which type of remake is a better fit for it.
Something like Spyro the Dragon, Crash Bandicoot, or Tony Hawk's Pro Skater? They're already 3D platformers where the relatively simple gameplay loop is great and doesn't need changed, so those types of games basically beg for the "new coat of paint" type or remake (so, improve them by recreating them in a new engine with better visuals, and up to date quality of life and feature additions).
Something like Resident Evil, Silent Hill, or the PlayStation era Final Fantasy games? Games with something between medium to very elaborate stories? Games which carry considerations in regards to controls (tank controls in the case of Resident Evil and Silent Hill), camera, or how they used certain assets (namely, pre-rendered backgrounds) to display the world? Games which lacked some modern quality of life things (voice acting)? That's when you enter into the conditions where re-imaging it has a lot of merit, even if the "new coat coat of paint" also does work. But I think while both are valid, it leans slightly more towards "if you're going to the effort, consider doing more for it" and the Resident Evil and Silent Hill re-imaginings show this wonderfully.
I would have welcomed a "Resident Evil 1 on the Gamecube" style of remake where it's just a remaster with improved pre-rendered backgrounds created from scratch... back in the 2000s or early 2010s. After all this time though, it would feel like a missed opportunity (though it'd obviously still be an improvement).
Also, I'm not sure if I entirely agree on the "remakes are hit or miss" part. From my perspective, it seems like the overwhelming majority of them in recent times have been hits, but... maybe I'm only looking at the successful ones and not aware of the bad ones? In any case, there way too many successful ones (and the majority of them are faithful), so I'd say Square Enix would have to like... either try to fail by changing it too much, or put way too little effort in... in order to fail at achieving a successful remake for this game (success being measured in terms of fan reception, not Square Enix's infamously high sales prospects). There's way too much obvious and accessible potential for a successful remake with this game and its characters/story in particular, and yes I'm biased but I still feel like that's the case with the overwhelming "proof" being all the other vastly successful game remakes/re-imaginings from that era.
Parasite Eve!
This era is honestly so full of franchises that didn't continue but would be worth a look, whether that's merely giving them decent remasters, or sequels and franchise revivals. Parasite Eve is one of them. Capcom needs to get on Dino Crisis 1 and 2. Why hasn't Sony done anything with Legend of Dragoon!?
I haven't actually played FFIX (but plan to sometime) so I only skimmed the post and didn't read any replies. That said, I think its unlikely to be turn-based, as they seem to have abandoned that altogether.
Tactics, VII, VIII, and X are the ones I've played and enjoyed, as I only did console gaming from 1995-2005ish. Everything after FFX failed to interest me due to the departure from Turn-Based. Anything from punishing you for being slow (FFXIII) or becoming straight-up spectacle fighters (all the modern ones).
FWIW I've purchased the entire franchise (excluding XVI and the VII Rebirth), but only finished the stuff from 2000+/- a few years. Maybe pick up the VII bundle in 5 years or so, but I don't really think Square makes games for folks like us (me?) any more.
Yes, the modern mainline entries have abandoned turn based battles (I'm putting ATB under this for the sake of discussion), and I think Square Enix infamously said turn-based is dead in the early-mid 2000s.
However, I lean the other way despite that and think a remake of Final Fantasy IX would likely use some form of turn/menu based combat because the real-time "Devil May Cry-esque" combat, and where your party acts via AI alongside you in real-time, wouldn't fit here. If you're not aware, part of Final Fantasy IX's thing was being an intentional throwback to traditions that the series was about to (or already had) move away from. It went back to high fantasy instead of sci-fi, it was the last to use ATB (Final Fantasy X retained turned based though), the last to use a world map (and pre-rendered backgrounds), it was the last that series creator Hironobu Sagauchi worked on, and the last that Nobuo Uematsu solely composed. So a modern remake would almost beg to fill the same "throwback" role, especially since turn-based is so absent yet there's a not-insignificant amount of the market crying for it. If ever there was a game to use turn-based in, a remake of this game would precisely be it. Using turn/ATB based combat would not only to be faithful to the original game it is remaking, but it would be faithful to the very role today that the original had back then. Being a throwback to old traditions. Therefore, I just can't see a remake for this working with the battle system they've used in the other modern Final Fantasy games, and I think (and hope) even Square Enix would realize this. The good thing is, the rumors (obligatory "key word" mention) were that the remake likely would be faithful and that the battle system probably would stick to what Final Fantasy IX was.
If you want a recent turn based recommendation, try Dragon Quest XI. It's by no means synonymous with what Final Fantasy IX is... but it's the only remotely recent thing I've played since then that comes close to resembling those late 1990s and very early 2000s JRPGs. Funny enough, playing that game was the start of what seeded my "we need a re-imagined Final Fantasy IX" desire. Seeing the other old games get remade since then (almost every one being successful), and the Memoria Project later, made me shed the remaining doubt.