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That's pretty much the gist of it - gone but not forgotten. There's nothing to say that "Ravenloft" doesn't exist however. It would simply take the form of a series of linked domains of dread somewhere in the Shadowfell. Nothing about that contradicts the original setting IMHO. It's easy enough to simply say that the original scribes/scholars etc. just had the whole "Demiplane of Dread" idea wrong, and that the domains described in the campaign setting have always been just one corner of the Shadowfell. Compared to past iterations of the game, 4E cosmology is fairly easy to slot new (or old) things into. 

Man, I gotta use that myself sometime! I haven't run any Ravenloft games since 2nd Edition, and a new Ravenloft campaign would be awesome... 

Several things were folded into the 4E Shadowfell, the "domains of dread" among them. They aren't necessarily assumed to all exist in a single geographical region, but nothing says they can't be if that works better in a given circumstance. (That said, there's no need for them to be geographically connected, since it's perfectly possible to assume that, in the right circumstances, you move directly from one to the other.)

  4E also operates on the premise that the world-like planes (the World, the Feywild, and the Shadowfell) as strongly interconnected, to the point that it's possible to move between them without needing special magic or portals if you find yourself in the right (or wrong) place, and the concurrent areas of each even resemble one another on a general level. (IE, walking down this particular forest path will result in you crossing over to that particular copse in the Feywild or vice versa.) This is a big change from the 3E Wheel, which assumed that even 'near' planar crossings were relatively difficult to pull off. Hence, you don't really need a separate demiplane to accommodate the the Ravenloft-style concepts.

community.wizards.com/nentir_vale/wiki/T...

This is a list of all the material released so far on the Shadowfell and notes where Ravenloft material is included. They seem to have been holding off for a full Ravenloft book, so the important sites, Castle Ravenloft and the other well known domains of dread never got statted out. Vecna has left for the Astral Sea, rumored to be lurking in Pandemonium the former dominion of Tharizdun.

Even as a fan of the setting, the normal world that suddenly gives way to a bleak expanse of haunted terrain I think lends itself to a better gothic horror drama, rather than the bizarre Dracula meets Frankenstein feel of Raveloft. I picture Barovia as a village that appears in the world but whose inhabitants don't even know they live in the Shadowfell, perhaps they even claim that Strahd's magic moves the forests beyond the hamlet.

We have a map of Barovia, which is now in the Shadowfell.  We have adventures there.  We have Vistani.  We have Count Strahd himself statted out.  We have Kas the Betrayer statted out.  We have Ravenloft character themes.  We have an idea of the nature of the Dungeons below Ravenloft through the board-game. 

All these together allows for everything except an original conversion.