yes there is goin to be another kingdom hearts game, and im sure everyone has questions about it, and yes ther are people making up rumors and stories about wut its going to be about. I've searched online and here's wut i've come up with so far.. these theories are 90% true. You can make out alot of it by the secret ending on KH2, here's wut it all says in the ending...
"The keyblade is said to hold phenomenal power. Our legend says its weilder saved the world, while another says that he wrought chaos and ruin upon it. I must know what the keyblade is. A key opens doors. 'Ansem'
-master of keyblade, the lost two, Memory of Xehanort, Chasers, Keyblad War-
It all began with... birth by sleep."
now first of all the three people you saw in the secret ending are NOT sora, riku, and kairi. it was confirmed by one of the game designers. the next kingdom hearts game is supposed to take place before kh1. now lets look at the clues in the secret ending.
The first part, "The keyblade is said to hold phenomenal power. Our legend says its weilder saved the world, while another says that he wrought chaos and ruin upon it. I must know what the keyblade is." it looks like Xehanort said this to Ansem when he was his pupil still. and Ansem replied "A key opens doors" now i could be wrong on that part, but it makes perfect sense...
I'm not sure wut "master of Keyblade" and "the lost two" are about.
"Memory of Xehanort" is probably before he met Ansem
"chasers" are probably a new species to fight, they go after your soul? idk i heard that from a website
"keyblade war," not sure how that comes into play...
then the last line "it all began with... birth by sleep"
idk, rumors from other sites are saying that birth by sleep is another type of species you have to fight, possibly chasers or maybe its how darkness and the heartless came into play??
if you want to see the english version of the ending go here ->
Linkpost your theories and info here