I was just involved in a discussion regarding 'Space Paranoids' and 'The Grid' and the potential of that world returning. Whilst, I flat out do not expect that to happen, this does tie in to something we know is happening within KH3 and that's cameos.
This has been a common occurrence within the KH series from Pinocchio in Traverse Town and the likes of Merlin and Scrooge McDuck in Radiant Garden. We know Remy will be in Twilight Town, so linking back to my original point and the question I want to ask you all, a Tron cameo would work.
During the second trailer at E3 and the Orchestra Trailer (for those who attended), Ienzo was seen in Ansem's Computer Room. We know Ienzo is helping Sora, and during KH2 we know Tron can communicate to the 'Users' via the computer. So why not have Tron speak to Sora or Ienzo? This is merely building upon something that already exists within KH and if we are focusing on Ansem's data, there becomes a valid reason for a Cameo.
This builds upon my next point, why limit Cameos to a small selection of worlds? If we have similar worlds and by that I mean a world that has not made the cut, why not have them appear as a cameo in the world that did? Now the Tron cameo is what I'll call a direct cameo which is where there is actual interaction with the characters, however you could have indirect cameos such as the lady and the tramp statue again.
Another point I think is interesting is that it encourages exploration of the worlds. For example in the Pirates world, why not on one of the islands have an indirect reference to Atlantis? Have a 'Hero's Duty' console in Toy Box (I believe this would work the best due it being sci fi) and in Tangled if we can explore the caves, why not have a bear painting?
Overall, what do people think? What Cameos would you like to see? This isn't my usual 'think of a theory' post, but more of a discussion!