I kind of like the idea of Marluxia's somebody acting on his own devious plans. It's never really been explained that a Nobody is only able to control lesser Nobodies, so surely his Somebody can take control. However, I just feel throwing him in as a subplot would be too out of place. It'd make more sense if he had a role in the major plot.
Heartless are still around, and we still have Nobodies. Other than just being present, we have to assume they are being controlled in some manner whether it be Xehanort's Organization, Malefecent/Pete, or a third party. I would say Disney villains in their own worlds, but usually it's just the Darkness and/or Heartless taking advantage of them.
Oh, the subject. Well, I will say I'm getting anxious on NA Unchained Chi details. The last 2.8 trailer has me very interested in Back Story, so I really want to experience Chi on the NA side soon.