A lot of people would feel like it would be unnecessary, which I sort of understand but I know everyone wiuld buy a KH remake of any one of these games the second its announced. Plus, it would be an opportunity to fix some continuity within the KH universe to make the rest of the storyline feel more streamlined for average casual players. Keep in mind, not everyone reads the journels or look up Ultimanias like us type of fans do. So certain plot elements that are theorized and found to be true or not within earlier games is obvious to us but not to the average player the more they go into the series. If there's one thing KH has major problem with is how it tells its story. Its unique but not always well understood, espeically when we get to KH3 where some things just make no god damn sense at face value.
Bringing in a lot of retconned lore of the later games or take them out to make things seem less out of place in the series. Though I understand fans being against this since, besides KH2, KH1 is the second most beloved game and it having a more simplistic tone and themes is what people like about it. But I don't honestly think it would really complicate things or mess with the tone as long as you don't reveal too much but things like Sora being said to be the chosen keyblade wielder would definately need to be taken out since it's kind of immediately retcon by the end anyway. And though its said that other keyblade wielders exists in journels and whatnot, the average player isn't going to know that. So I wouldn't be surprised if going into KH2 when Riku and Kairi suddenly get brand new keyblades out of nowherethat don't look anything like Sora or Mickeys would have fans logically straching their heads.
Maybe also fixing the issue or maybe just addressing why The Organization is so obsessed with Sora since he really isn't all that special in the grand scheme of things. It's never really said in game what happened to other keyblade wielders pre-BBS (and even in that game, they don't explain it either lol) but apparently they do still exist and are just scattered across the universe... I think? And since Union Cross and Dark Road are still ongoing, the question of what happened to most keyblade wielders is still not answered and a lot of fans just assumed most of them simply died off and rest are just separated but that doesn't feel like a satisfying conclusion. There's a whole gap of time between both these games that's unanswered. I do think its something that will be addressed in Dark Road and Union Cross but obviously more needs to be explained or at least hinted at to justify a group of adults going after this one kid so hard since if keyblades can just appear in your hand out of nowhere (according to KH2 anyway) then why is Sora's keyblade the one they need when they can just go find someone that's less of issue for them and they don't have to spend a whole year trying to search for so that can maintain control over Roxas. Maybe its irrelevant to some but I feel it would explain a lot of things or just explain why Xehanort and the Organization go after Sora as much as they do even though he's no different than any other keyblade wielder. I don't know, maybe manipulating a kid and his nobody is a lot easier but I feel we can add some lore to go a little deeper then that.
Also, making the story of the nobodies feels less like a retcon when we get to DDD. Obviously there are things that hint at the reveal throughout the games but those hints only became hints because DDD made it so. KH2 presents the story of nobodies as if Roxas and Namine being inside Sora and Kairi was a good thing by end but the rest of the series contradicts the ending themes of KH2. Which, to be honest, KH2 has some pretty weird themes in regards to Roxas and Namine and nobodies in general and though it makes me believe that Noruma had the reveal of the nobodies growing hearts already in his mind the whole time, the way its presented in KH2 compared to the rest of the series is a bit weird to be honest and maybe he didnt think all the way through at the time.
It would also be an oppurtunity to improve the Disney plots, make them more connect to the plot and not just a select few.
Also in COM, taking out the smell of darkness since that never comes at all. I could name more but I havent slept very well, so bleh
But thinking it more, I would rather they focus on new projects. I think the series is in a fresh starts right now and though I have reservations about about the games that are announced so far, I think it's better then going back and remaking a bunch of games that are already available on most consoles anyway.
Also keep in mind, KH has A LOT OF GAMES. When it comes to remakes, not even Resident Evil or Halo or any other mainstream franchise match the amount of games that are interconnected other then Metel Gear Solid. Both that franchise and KH are unique in this aspect of gaming, as they play out like Harry Potter or The Marvel films with each one continuing ongoing storyline for a long period of time and ranking multiple entries to tell a unique story in each one. Remaking one game means that at some point, you have to remake everything up until KH3 and at that point, that feels like a lot of development time that could've been toward something else.
And with MoM, Dark Road, the upcoming FF7R Part II, and two unaccounced KH games, Noruma has enough his plate with out worrying about a remake or several remakes that would logically follow since the first remake would no doubt make buckets of money that would make Scourge Mcduck have a heart attack.