is it really a good idea to do an overhaul of the setting?
Since even the fans acknowledge that the setting was sometimes hard to use for more than one-off games, I'd say yes.
The only reason to release Ravenloft is because it has a built in audience: hard core Ravenloft Fans.
Or you do it for the same reason they released Expedition to Castle Ravenloft: Because at its heart, Ravenloft has some really great ideas, some classic villains, cool set pieces, bitching monsters and style to spare.
It probably isn't going to appeal to people outside of that group as much anyways, so why meddle with it?
The people in that group already have their Ravenloft material and are hardly guaranteed sales. They aren't super-relevant in terms of strategic planning.
I'll be honest here, the only reason why I like Ravenloft, and would love to see a 4E version, is because it was the first game I ever ran; I grew up running Ravenloft Modules, reading Ravenloft Novels, and Absorbing the Van Richten Guide Books. I think what they should do for things like Dark Sun, Spell Jammer and Ravenloft, is create a "Classics Line". They should keep the fluff relatively untouched, but update the mechanics for 4E.
That kind of thing is really best left for Dragon/Dungeon articles, IMO.
An actual line needs to be able to be picked up off the shelf by someone who's never heard of it before, its awesomeness immediately conveyed and able to be taken home and used without having to rethink how D&D is played by the group before it can be enjoyed. (Further afield stuff is better left for third party publishers like Mongoose and Goodman, both of whom are straying off the reservation from the PoL setting.)
Ravenloft is (yet another) the original Points of Lighting setting: Player characters and the few non-hostile NPCs huddle together around their guttering flames while a world full of indifferent-at-best (but probably hostile) THINGS wait out in the darkness. Beating back the darkness is a temporary victory at best, and escape is almost unthinkable.
In previous editions, Ravenloft needed a whole bunch of tacked on new rules to stop the players from just reaching for the Players Handbook and saying "I've got the answer right here -- NOOOOO problem." But 4E removes most of those Get Out of Hell Free cards from the table.
I think relaunching Ravenloft would be terribly easy: Just create an anthology of baronies, islands and the like (many of which would formally have been seen in previous editions), but instead of creating some sort of Evil Soup they all float in, let them just exist in their own standalone (or contiguous) environments in the larger context of the World.
Darklords always had their own quirky ways of closing off their domains. Most (or all) of the villains in the Ravenloft anthology book would have a similar power. But while in previous editions, many player characters knew these were all linked together in some fashion, utilizing the underlying "mists of Ravenloft," there would be no such assumption that this giant briar hedge was related to that army of watching wolves or those vanishing paths up the mountainside.
It could still all be optionally linked together somehow -- Strahd or Azalin, as always, provide good mechanisms for this -- but I see no problem with dropping in any of the old domains into even a perfectly ordinary setting. Heck, depending on how dark and dangerous the wilderness is in your campaign, you could enjoy the prospect of your player characters running eagerly into a darklord's domain ... for "safety."
The cosmological underpinnings of Ravenloft might have been interesting to speculate on, but I'll bet that most games actually revolved around surviving and escaping various domains. And that ports over extremely easily.
