I *think* AtW figured out the whole process for how to awaken all the hearts that are
asleep, even the ones like Roxas and Xion. My understanding is that Roxas and Xion have hearts that are completely their own now(especially since at least Roxas has tried to reject his connection to Sora before and Sora in DDD rejected Roxas's "I am you" statement), which means that extracting them shouldn't be any harder than awakening Ven(minus the bodies part). Getting Aqua out of the realm of darkness would be as easy as opening the door like they did at the end of KH2, but the hard part would be assuring that she reforms where they want her to, not, say, in the Room of Sleep where her armor is. Personally, I think a lot Terra's fight will be TERRA'S FIGHT and with some help from Aqua and some MX pummeling he shouldn't need a whole ton of work. I kinda think you're overcomplicating it
That said, I just stared at Youniquee's sig for like twenty minutes and now I'm freaking out a little. In that scene (which may not be completely cannon or anything) after Sora does his big fancy keyblade swing, everyone else does something similar and then just POOFS INTO PAPER with the exception of Riku, who poofs into paper while reappearing at Sora's side. Now I'm reading way too much into that, but I can't help but wonder whether or not our seven lights will become permanent individuals or not...
That's how it turns out. While he was DiZ, Ansem the Wise continued to do research on hearts and Nobodies and it's implied that he found out already at that time about the possible heart-growing, but choose to ignore it at first due to his prejudices against Nobodies and his drawn out plans for revenge.
Yep, Roxas and Xion (as well as Naminé too) gave birth to and developed their own hearts where their own consciousness can reside since they're in essence independent entities from Sora with their own identities. Roxas was always struggling to be his own person and Sora himself also always saw him as a person of his own, just like he treats Naminé as different from Kairi or the Riku Replica as different from the real Riku and sees in them their own people.
That was all already hinted at in Chain of Memories:
Sora to the Riku Replica said:
Sora: Wait! Who cares if someone created you? You are you and nobody else. You have your own heart inside you. Those feelings and memories are yours and yours alone. They're special!
That's what Ansem the Wise also explains to Riku in the ending, what makes Sora and his heart special. He sees the good before the bad and simply doesn't care
how a being was born, he treats them as individuals who deserve the same privileges than he has to live freely.
His speech to Roxas was practically the same in meaning as what he said to the Riku Replica in CoM and that's what provoked Roxas' surprised then changing to happy reaction.
As for them getting bodies, Kairi gave Sora one in KH1 when restoring him, so she (or the other Princesses) could probably conjure a vessel for each Naminé, Xion and Roxas to inhabit.
As for the scene from Youni's sig from the opening, it does not show the whole crew.
In the actual scene Riku, Mickey, Donald and Goofy
don't poof into paper because they are already available and fine. Terra, Aqua, Roxas and Ventus poof into paper at the end to symbolize that they are not fine yet and still need to be rescued.
