I'd say it'd need less of an overhaul than other worlds. The setting was never as hard into the limits of what could or could not be done as other worlds. Unlike Dragonlance, which used the backstory and organizations to justify arbitrary 2E rules and conventions, Ravenloft always seemed more open with which rules worked. The VanRichten Guides are obsolete now, but then they always were.
The big changes are races. But demihumans have never been a large part of the world so no one notices the removal of gnomes or addition of tieflings.
The latter, along with warlocks, work really well with Ravenloft although they might be presented as people who were human then transformed or the children of people who made infernal pacts or had dalliances with the inhuman.
The only really big problems I can think of are threefold.
1) Necromancers. These were big in Ravenloft. There's at least three wizards that specialize in undeath. But, since its very, very, very unlikely that we'll see a Ravenloft book anytime soon we can wait for them to add a necormancer class or Death power source.
2) Dragonborn. They simply don't fit the world. At all. So *poof* they're not there.
3) The planes. A larger change but explainable.