Yes I am not a big fan of the card system either. And that's not because I don't like playing it, but more because I see everyone skipping this game because of it. That's a design flaw to have people watching cutscenes on youtube rather than playing a game. This need to be addressed at some point.
For days, I am not sure. The game has been known to be repetitive with the missions and all and it wouldn't fit well on a console I think. A shorter version of it could be more impactful and more epic. But then, how do you develop the friendship between the trio without showing their day to day life? Days is a tricky one for sure.
But I am convinced that with full remakes, the entire dark seeker saga could fit on 5 games rather than 10 if smaller entries are fused properly.
I am one of those youtube people 😶
For days, maybe the more repetitive, unimportant, unimpactful missions can be skipped. Lots of Union X levels weren't required so it'd be like that.
Kh1 and CoM can be fused. After the final scene of kh1 the first scene of CoM starts and you play that game as if kh1 never ended. Episode Riku can be played from the main menu.
Kh2 can be its own game with 358/2 Days being accessed through the main menu.
Coded is a tricky one. I think it makes the most sense for it to be accessed through the kh1 menu even tho it takes place after kh2. Maybe before you start Coded you'll get a short warning screen like "This game is best played after Kingdom Hearts 2. Are you sure you want to proceed?"
Bbs and 0.2 can be combined and the final and secret episodes of Aqua's story will not have to have any work into being unlocked and 0.2 can be merged into Blank Points. No menu is needed.
DDD can be its own game but the cutscenes that take place in the present time in 0.2 can be put into there.
Unchained/Union X and X Back Cover can be merged. Missing Link and Dark Road can be accessed from the main menu.
Kh3 and the main part of Remind can be combined. After defeating Xehanort, all the guardians decide to meet up at the beginning of the world Sora is the last one to leave and you take him to the place where the cutscene in which he decides to save Kairi happens, and the rest of the segment continues from there. The Luxu/Luxord convo, the MoM/Xehanort scene, and the Organization meetup can all be moved to different parts of the game. The limit cut and the secret episode can be accessed from the main menu.
MoM is fine as is.