They don't call him Master Yen Sid for nothing. It's even seen in Birth by Sleep that he trains Mickey and, during KH3D, took Sora and Riku under his wing. It's just that, Eraqus, Xehanort and Yen Sid all went through their separate ways:
Eraqus had to stay as Master, seeing as how someone had to guard over the Land of Departure, and at the same time, he took two students.
Xehanort renounced as Master and traveled the worlds, studying the origins of the heart, and at the same time, he took a student.
Yen Sid stayed as Master, tutoring Mickey and observing the universe at the same time.
Knowing Yen Sid, I presume he'll ask Mickey to teach her along the way, experiencing things first hand. Unless, of course, he plans to use the Realm of Dreams as a means of training grounds (she could also learn some team work from the little Spirits).
Mmhmm, he'll replace Terra, seeing as how Xehanort hinted he's in the Organization.
No. Next game will be KH3, seeing as how that, in the ending, it's displayed as KINGDOM HEARTS 3. Both Lea's and Kairi's training might be referenced and touched through Memoirs, that is, if they return.
It doesn't have to be a trio, but with how they seem to be a staple in the series, it's much likely possible that a new group of protagonists will very well be a trio.
Invent a new villain with a different backstory to Xehanort's and different motives.
Everything there is to the history of Kingdom Hearts has been explored, but that doesn't mean they can reuse these concepts with new things.
With how TWEWY was included, I'm inclined to think they're considering the possibility of adding SE games worlds.
Now that you mention it, I just pictured Master Xehanort taking Sora to witness the Keyblade War. They share a few thoughts and finally decide to fight.
This makes sense, but he shouldn't receive the bill. But we'd have to do a small research of that country's politics as to who receives the bill in these sort of circumstances.
Uh... Nomura himself said that BbS isn't a spin-off, but a mainstream title. A brought this because he called that game KINGDOM HEARTS 0, seeing as how it's the beginning of the series, the start of the chain of events that caused a reaction to other games.
Like I said; KINGDOM HEARTS Birth by Sleep (KINGDOM HEARTS 0) is the origin of the series (and as far as Nomura said he'd go into the past of this saga).
I'm going to try and picture a game centered in this:
NAME: KINGDOM HEARTS Keyblade War PROTAGONIST(S): Those who want the light for themselves. ANTAGONIST(S): Those who want the light for themselves. ENEMIES: It can't be Heartless because they haven't crossed the Realm of Darkness. Nobodies either because they started to exist once the Heartless entered the Realm of Light. Unversed because Vanitas isn't around and... Dream Eaters? I think there isn't a way out for them. They could also try an entirely new enemy, which I doubt this angle is going to be taken. PLOT: Everyone gets greedy and want the light for themselves. :v
Scratch the part of protagonist, they're all antagonists.
I'm not saying it couldn't work, seeing as how SE can make anything work, but I have serious doubts about it. We're close to the ending of the saga, bringing and stalling attention from what matters right now (Xehanort) would be kinda dumb. Obviously, the war happened even before Xehanort was born, seeing as how the event occurred before the worlds were split afar and during Xehanort's MoM, they had to use the Lanes. Other than that, we know what's there to know about the war:
+ People star fighting for the light.
+ The Xblade appears.
+ Kingdom Hearts appears alongside it.
+ Something happens that creates a destructive aftermath, breaking the Xblade in twenty pieces and Kingdom Hearts to the Realm of Darkness.
+ There are two ways to forge the Xblade.
Wow, a boob was revealed. '_' That's pretty dishonorable right there, yep. People accidentally showing part of their body to the world is something even the king of Spain does not tolerate... *ahem* In all seriousness, it's just a part of the body everyone has seen before. It's not like it's much of a deal going around showing your boobs, seeing as how that, if the people of San Antonio have the maturity to keep on with their lives by being surrounded by naked people, why not be mature to something as small as an accidental boob show? It's not like it's dishonorable to see a mother giving breast to her child (although two different scenarios, but the essence is the same; keep up with your life, there's nothing wrong in showing your body parts).
Actually, in KH3D, he's named the most powerful of the Keyblade Masters.
It has always happened since the dawn of its introduction to video game plots. '_'
They could just be former characters with confronted with altered looks (yellow eyes, pointy ears and tanned skin). The only reason Xehanort corrupts them is to make them Keyblade wielders of the dark, he has no control over the appearance changing effects.
I wouldn't go as far as calling them copies, seeing as how they all have their own persona (even though they share Xehanort's mind). Other than that, they're just corrupted.
What do you mean? There are two ways to recreate the Xblade:
+ Clash a heart of pure darkness and one of pure light;
+ Clash seven Keyblade wielders of light and thirteen of the dark.
Xehanort went by the first route and failed, now he's using a plan b.