well we dont how long kh3 going to be all wee know nomura saidkh3 is very overwelling big which is why the aqua stuff was cut out of kh3You really think they can fit all of that in 1 game? Sora saving the worlds again, saving TAV, training Lea, training Kairi. Maybe assemble the 7 PoH for the final battle (I'm not sure if that's needed, but Xehanort needs 7 Hearts of pure Light). See what happend to Eraqus in Terra's body. Have the flashbacks from Eraqus and Xehanorts past, see what happend to Luxu and MoM and how they got in contact with Xehanort (that one is speculation and could also be shown in Ux). And between all that they also have to show of the Disney Worlds. We will probably get some mini games and Gummy Missions too. Maybe even Pooh's world again. Like sure, KH3 is going to be great, but can they really fit all that in the game and then make a whole new storyline where they fail to save Ventus and they have to deal with Venitas again. After wich they have to introduce a new Keyblade Wielder to take the place of Ventus. Skuld, Emphemer, Yen Sid. That are the three I can think of from the top of my head. From wich 2 are from the past and the third is retired. It's a fun thought, but I don't they could do that in just 1 game. And I certainly don't think they way they have to save Ventus is easy. Xenmas agrees, he has been looking for that room for over a decade as well.
Yen Sid said that Ventus needed his friends to awaken again, so I always just assumed that they first had to rescue Aqua, then they had to save Terra and then they could awaken Ventus. But after DDD I guess Riku and Sora could do it too. Kinda nullifies Yen Sid's line though.