Honestly, I'd be really interested to see how a remake of KH1 would turn out, whether it'd be like Ocarina of Time 3D where it uses new assets from the ground up but still very faithful to the original or a full-on reimagining like how FF7R turned out, which I'd be fine with either of those scenarios. The story of KH1 is such a classic, it's no wonder the series was given two opportunities to revisit that story and its settings with CoM and coded with their own twists. I'd even argue that the beginning of DDD was another stealth reimagining of at least the beginning of KH1, which brings me to my next point.
I've been playing around with this idea for years now even before KH3 came out, and I still think it could work now that we're in the 2nd Phase. Personally, something that I'd wanna see in a full-on "hard reboot" of KH1 is for the game to begin mostly similar to how it was in KH1, including Dive to the Heart, Destiny Islands, Disney Castle, and Traverse Town, with some small yet noticeable changes being thrown at the player already. Basically like the beginning of DDD, but on a larger scale. The following is a list of changes that could happen during this segment.
- Who appears on the stained glass pillars in Dive to the Heart? Are they the Princesses of Heart again or do they show the New Seven Hearts instead? Or do they depict something entirely new?
- Will the FF characters in Destiny Islands and Traverse Town remain the same or will they be replaced with other Square characters or even new original characters instead?
- Who does Sora meet in the small cave at Destiny Islands? Is it Ansem SoD again? Or maybe it's the Master of Masters?
- Whoever Sora meets at Traverse Town, how will they explain why the Keyblade is connected to him?
- Why did King Mickey leave Disney Castle? Will Donald and Goofy find Mickey sooner than they think?
- How do Sora, Riku, and Kairi end up leaving Destiny Islands this time? Are they gonna end up staying separated the majority of the game just like last time?
Then after Sora leaves Traverse Town, the journey going forward ends up being nowhere near like how it was in KH1, complete with all new Disney worlds and a new threat unrelated to anything contained within the Dark Seeker saga of KH. And throughout the game, there are hints littered throughout the game that tells the player that this might not even be an alternate universe or different worldline that the player is experiencing and may actually well be a stealth sequel taking place within the main timeline. One subtle example could be how even though Sora, Riku, and Kairi are depicted in their KH1 ages again, all three of their hairstyles are how they were in KH3 and that they wear all-new outfits like every other numbered title and DDD. It only takes up until the game's secret ending that it all-but confirms this really is a stealth sequel after all and leaving a huge enough hint to give players ideas on how this "reboot" connects to the timeline.