I'm really looking forward to seeing that. Do you think we'll get to see this in the main series or do you think there's a possibility that they'd get their own spin-off series?
That will depend on how the next/new saga is structured. If they choose to keep the "only one playable character"-scenario it depends on if they allow a fully fledged party system for team mates even if computer controlled, then we would see it in the main series when adding Xion, Roxas (or anyone for that matter) into your current party.
If they decide however to allow players to
decide who's the party leader we might even get to experience the new/evolved battle styles firsthand by controlling the character.
There's another possibility though, one I realized recently when remembering that we have effectively
three main Keyblade Wielding trios and
three main branches of consoles so far: Sony home consoles, Sony handhelds and Nintendo handhelds.
It could be possible that while the story of all the characters is still connected and they work together, they have to fulfill different tasks/assignments in different sets of worlds, only occassionally meeting each other. This would result in each platform getting designated a trio, with the other two trios only appearing as cameos in the given installment. For example, Roxas, Xion and Lea would be the designated trio for the Nintendo titles, SRK and TAV only appearing sporadically in their titles and vica versa.
Xion's current fighting style may have to do with Xemnas programming her to physically be Sora. At this point she actually has her own heart, so she may develop a completely different fighting style as her heart matures until it is 100% her own.
Correct, although for her heart to develop further and mature, she needs to
exist again first, just like Roxas and Naminé.
As seen with Ventus after Sora saved him in the BBS Prologue, his heart was still not fully formed (direct quote from Nomura, BBS Ultimania) and the four years between the birth of Vanitas and the actual plot of BBS served to nurse Ven's heart back to health.
Indeed, I'm curious to see how it will differentiate later on is all.
I reckon they will, I mean it would be a waste to bring all these characters back that are for all intensive purposes main protagonist just to bump them down later on. Lea is a bit of a disadvantage isn't he (or is he?) since he has to readjust his style when using the Keyblade. Xion's style changing is more for the sake of variety while for Lea it's out of necessity. Then Kairi has has to learn from scratch although she doesn't need to make any adjustments. Hhmmm style all around!
*throws style sparkles*
(╯°□°)╯*:・゚✧ ”
Exactly, it would be a waste to invest so much in those characters and have Sora and co. go to hell and back to save them only to have them either pushed to the sidelines completely, or as some people actually propose, have them die or vanish again.
Lea seems to have talent though, and considering his battle style with the chakrams was pretty heavy on speed as well as mid-range battle, I guess he could easily adapt into a style that is a sort of mix between Riku's and Ventus'.
Kairi will be interesting to observe, I would hope she gains something really unique as her main battle style (probably a sort of fencing style?) and not just a rip-off from Aqua's style.