I bet you that the lore we're gonna get in this place has DEFINITELY got to do something with Humans, and pretty sure not with Ancients or Dark Matter... Why humans, you ask? Weeeeell, it's pretty interesting that the only human in the Kirby Series we've seen so far is Adeleine, but we yet have no answers or questions if she's the ONLY human left... There's gotta at least be something what happened to the humans.
I don't think that DDD, MK, or Bandanna Dee will make a major appearance in the new game. Why? Because in the last puzzle picture Kirby seems to be setting off on his own and I think they would've shown off other characters (unless they haven't rigged their models yet, which is unlikely) This is also a new era for Kirby, so this could symbolize Kirby maturing to the point where he can go off on his own.