The closest we've gotten to a KH without Disney are arguably 0.2 BBS and Dark Road (so far) since they weren't in your face the whole time. Particularly in 0.2, it has dark twisted versions of Castle of Dreams, Dwarf Woodlands, and Enchanted Dominion appearing with none of its inhabitants to be seen and Mickey, Donald, Goofy, and Yen Sid being the only Disney proper characters to appear. While I think Disney not being in Kingdom Hearts at all wouldn't feel right, I think more experiences like 0.2 and Dark Road going forward would be pretty interesting. Just enough Disney for those who want them in while allowing more original lore or even more Square crossovers to be in the spotlight consistently throughout the stories.