Just a little theory: What if both the Unversed and the Dream Eaters could come back in KH3? I have facts to support this:

 

Unversed

-Vanitas showed up in KH3D as a vision created by Ventus' heart, causing Sora to see him.

-One of the chess pieces on the side of darkness, which was shown in the KH3 E3 2015 trailer, was the Keychain to the Void Gear; this little bit may heavily imply that Vanitas is one of the 13 Darknesses.

 

Dream Eaters

-At the end of KH3D, Sora noted that he was back in the real Traverse Town, and then his Spirit friends came to say goodbye to him.

-Young Xehanort straight up summoned Hockomonkey in Traverse Town, proving that he can not only create the Nightmare Dream Eaters, but control them as well. Even if they don't completely meld into the real world, the 13 Darknesses could just take the Nightmares out of the Sleeping Realm via Time Travel (because, as we all know, Time Travel in KH is not hard to understand AT ALL).

 

What do you guys think about my little theory? Do you agree or do you think only the Unversed could return?

Its true that they're original enemies

for the Toy Story world, but the question is which category do they belong to. Heartless? Nobody? Unversed? Dream Eater?

I would say possessed objects like the statues in beasts castle. The possessor heartless go in, control, and fade away when they are defeated.

Edited August 20, 20178 yr by IAMME

I would say possessed objects like the statues in beasts castle. The possessor heartless go in, control, and fade away when they are defeated.

Its possible, but they lack the common heartless traits (back + yellow eyes for pure bloods and heartless symbol + yellow eyes for emblems). 

So far Square Enix has been consistent with their character designs, and the closest thing those mech's look similar to are the Unversed.