I think that would be incredibly alienating for the Disney+ audience. That's almost 20 years of build up, lore, and character development to include in 12-13 episodes on a medium that houses people who aren't familiar with the series. Not to mention a Kingdom Hearts TV series primarily set in Shibuya would be missing the key component to what would entice Disney+ fans to watch - that being Disney worlds, characters, and stories.
Which is why a flat out reboot / reimagining works best for the medium. Anything that isn't that faces the alienation issue, as I feel like people would much rather watch a wide-eye boy teaming up with Donald and Goofy to help Alice in Wonderland, Aladdin in Agrabah, and Ariel in Atlantica than a confident boy with the strength of his 10 friends being in what may be purgatory after defeating one massive, universe ending foe.