Hmmmm.... I've been thinking about this, and how we might minimize the continuity-problems if they
do recycle Ravenloft's domains as Shadowfell "domains of dread". Certainly we don't want the game-setting shattered permanently, but OTOH, it'd be prudent to accomodate future gamers who might discover they
like spooky adventures, based on a successful 4E Weekend-In-Hell scenario.
Granted, I don't know much about the Shadowfell. I have yet to buy any 4E materials, and haven't even kept up on the online information since the Big Three 4E books hit the shelves. (I'm not rejecting it out-of-hand or for lack of funds; I just don't want to have to edit 3.5-based material for the sea monster book,
and learn the 4E rules at the same time.) So it's possible that this idea is incompatible with the 4E end of things.
But, looking at the problem -- the unpleasant possibility that they'll be presenting each of the old domains as an isolated, dark enclave within the Shadowfell, good for a one-shot escape scenario -- it occurs to me that the canon Ravenloft products already
describe a pivitol event that could, with a little tweaking, reconcile that exact situation with our own version of Ravenloft's history and metaphysics.
No, I'm not talking about the Time of Unparalleled Darkness. I mean the
Grand Conjunction.
Looking back at the final GC module -- the one in which the Land of Mists was
temporarily disrupted -- we can see what happens to several of the darklords: they slip out of Ravenloft to Prime Material Barovia, appear on a few wandering-monster tables, then are drawn back into their old prisons when the Conjunction fails. But what was actually happening to their
domains, while they were gone? Survivors of the Upheaval tell of seismic activity, realms vanishing or moving, and the Mists spreading over whole regions. That's what it was like in-character, but what was the
OOC effect of a domain's darklord taking a powder?
What if the Grand Conjunction actually expelled the domains whose lords had departed entirely from the Land, and those chunks of orphaned terrain punched through the boundaries between the 2E/3E and 4E cosmologies? (We know that the Mists can cross between cosmos as well as planes, because they stole Odaire from Gothic Earth and Meredoth from Mystara, neither of which necessarily conform to the Great Wheel.) As the 4E version of reality doesn't include an Ethereal Plane, these dispersed pieces of land would've settled in the Shadowfell, as the Ether's nearest 4E counterpart. Distracted by the Upheaval's chaos, few residents of the domains would have had a clue what was happening, let alone where they'd gone. To the creatures of the Shadowfell, the domains would have come and then gone again -- sucked back into Ravenloft as soon as their darklords were recaptured -- too quickly for the natives to infiltrate these new realms.
Ah, but what are the odds that WotC's versions would leave out the lords of these recycled "domains of dread"? Of course, they wouldn't pass up the chance to re-use such interesting villains, if they're re-using the lands they reign over ... but who says those 4E darklords have to be the
real ones? As I understand it, the Shadowfell is a place filled with the dark reflections of the material world's realms -- their terrain, their cities, their landmarks -- which embody everything ominous and creepy about the features they correspond to. It's a bit like how ethereal resonance works in 3.5 Ravenloft, when you think about it.
And in the case of a Ravenloft domain, the land is, itself, a reflection of the darkness within its lord. So what do you get if a
reflection casts a reflection...? If the Shadowfell spontaneously births an embodiment of everything that's darkest within the newly-arrived domain?
You get a
pseudo-lord. Not the same being as the original darklord, but a duplicate with a roughly-similar demeanor and history, that can take over as lord of the Shadowfell-trapped domain until it's drawn back by the Grand Conjunction's failure. Their powers might be a little different, their backstories simpler and their villainy more one-dimensional, just as sites' reflections within the Shadowfell aren't perfect copies of the originals. They might, in fact, turn out a lot like, oh, say ... a brief online Dragon article's simplified and 4E-converted versions of our own beloved BBEGs.
So when the Conjunction hit, and some of the darklords fled, the domains they'd abandoned were scattered through the Shadowfell of the cosmos next door, where pseudolords sprang into being. They linger there, scattered in space and perhaps even in time, for as long as it takes the Conjunction to short-circuit and the DPs to track them down. Long enough, in fact, for a lot of one-off adventures to take place, as 4E PCs stumble upon them! The resident "lords" aren't genuine, so can be slain by 4E heroes with no lasting consequences for the Ravenloft setting; indeed, the death of a pseudolord might well be the very thing that
attracts the Dark Powers' attention to their misplaced hunk of real estate. "Kill the lord, the realm disappears", right? The very cliche that haunted the old WiH era can be the thing that keeps our own Land of Mists
intact, under this interpretation.
Of course, there'd have been hitches in the post-Conjunction repair process. Gwydion's attempt to bust loose interfered with reassembly of overlying regions, so Markovia and G'Henna couldn't be put back in the same spots. Nathan Timothy wasn't recaptured until
after Arkandale, and by the time he was found, his domain had already passed into his son's hands. The domain of Zherisia plunked down in a part of the Shadowfell so hostile and aggressive, its countryside had already been invaded by the time the Conjunction ended; rather than import a horde of Shadowfell trespassers to their pet demiplane, the DPs retrieved the city of Paridon and left the rest of Sodo's realm behind.
In the aftermath of the Upheaval, the recaptured darklords questioned their minions about events in their absence, only to be told that their underlings didn't recall their masters having gone away. In the weeks to follow, the DPs judiciously edited peoples' recollections of the Upheaval, to ensure their great experiment (or whatever) wouldn't be contaminated by memories of their lands' brief sojourns in the Shadowfell ... or of the arrival of troublemaking outlanders with flashy 4E abilities.
Sound workable? Again, I don't know how well it'll fly, in light of my own ignorance about the Shadowfell and the 4E system ... and it might never be necessary, if 4E's "domains of dread"
aren't a recycling/looting of classic Ravenloft domains. But hopefully it'll get more people dreaming up ways to reconcile the upcoming article-series with our setting, rather than freaking out about the damage it might do.
"Who [u]cares[/u] what the Dark Powers are? They're [i]bastards![/i] That's all I need to know of them." -- Crow
But yeah, best not to take what little information is known, and then fill in the blanks with the absolute worst possible assumptions. 
