Nomura has actually stated KH3 will bring an end to the "Xehanort Arc" not that it's the end of Sora's story though.
Make way for Giga-pooh, the new villain with his side kick, Nega-Ariel, GONNA BE FINNY FUN BITCHES.
Either the Master of Masters is the original Xehanort, or watch all of this be set up by him to set him up as the antagonist of the next saga.
MoM is inside the box, it'll open in the climactic fight and he'll come out and be like "look you all fucked up because this isn't what I wanted to happen at all" He'll rip open his asshole and absorb xehanort inside of the bloody gaping maw and then zip off into outerspace where Sora and gang deiced they should be the ones to stop him, Queue KH4.
D23 game showcase live streaming currently. KH3 trailer at the end supposedly. Dunno how long it's gonna be or how long till KH3
https://www.youtube.com/watch?v=G1Xm5Arknfk
Edit: Showcasing Spiderman right now, supposedly KH3 is right after
Bump, KH shit just started
New world revealed is TOY STORY!!!!
WE TOYS BOIS
So much hype right now. Looks fantastic!
Taking over mecha suits? Fuck yeah!
COMING 2018!!
Coming 2018!
So really 2020
I was gonna say November but yeah probably 2020 lol