Dark Sun in 4th Ed wasn't a complete reboot if more retcon with some little details, as the new races. But this may be the best example to explain the challenge for game designers to new things, races or classes, to previous settings. Would you allow wardens and seers, 4th Ed new classes, to Athas? And the psionic ardent, , the lurker or the soulknife?
(and the time-travel has been canon in Dark Sun).
A crossover Jakandor-Dark Sun is possible but we allow ourself to break some rules. I don't talking about visitors from outer (but some githyankis did it) but people from Athas and Jakandor being sent to a third region. Athas is almost totally
disconnected, but not always it was like this. In the past, maybe before the genocide wars, some native from Athas could go to other zones.
We know nothing but I have suggest in the past the idea of a megaevent linked to all settings, like marvel secret wars of infinite earth crisis by DC to justify some retcons and changes in the continuity and metaplot, with the chronomancers and time spheres as excuse. This idea needs time, and maybe future titles in the main media could cause alteration in these stories.
Some Ravenloft novels aren't set within the land of the mists but in some regions from the prime material plane. I guess we could see more modules set in these zones, totally unknown for us, without links with famous worlds (FR, Grayhawk, Mystara or Krynn). These modules would allow different endings aren't possible in Ravenloft, for example a villain could be forgiven because he face a worse menace, or to start a undead apocalypse. Any modules wouldn't be within the demiplane of the dread really but in certain shadow domains, special demiplanes in the shadowfell (canon in 4th Ed).
I have published some pictures because I have thought they could be useful as source of inspiration. If you want to be really creative you have to be openedmind and to drink from multiple sources and after mixing all in a idea storm. Ravenloft has to be loyal to its true roots, but also allowing different styles. Somebody will want something like Nightwish or Within Temptation, but another would rather stories like ones from a videoclip, or AMV, by ERA, Enya or Avril Lavigne singing "Don't let me drown". Somebody will want tragic stories about characters too proud to do the right choice, but others about facing internal fears and challenging tragical fate at least with their sacrifice help to a better tomorrow for other people, with some pieces of hope.
I would be Universal producers may ask a island of terror with XX-XXI look (furniture, fashion and technology) to create a horror serie as Dark Shadow (reboot soon), the mash-up of Sabrina the teenage witch or American Horror Story. This is possible if we allow abductions from other worlds as Gothic Earth (Masque of Red Death), Gamma World or Dark*Matters(d20 Modern), or mini-setting "Age of Adventure", "Shadow Stalkers" or "Pulp Heroes" from d20 Past.
(Hexenbiest from Grimm serie, she isn't an undead)