I still hold out hope that they don't use Ravenloft the way this article talks about.
Seconded/Agreed.
The "negative energy border plane" to offset the "positive energy border plane that [they are making] Faerie", would/should be the Plane of Shadows.
Ravenloft is a demi-plane. I, personally, would make it a "bubble" in the Ethereal, but dif'rent folks could/might want to make it a bubble in the Plane of Shadows...or a bubble in Tarterus...or, even, a bubble off the Prime Material [of whichever world you inhabit].
The "Shadowfell" [tm] would be another, different, demi-planar bubble floating around in the Plane of Shadows, touching Primes hither and thither.
Like the Plane of Dream is, I think, a demi-plane. A bubble of Dream [altered consciousness] abutting the Prime...perhaps also adjoining Faerie in one part and Shadow in the other (for where nightmares -the "bad dreams" not the "demon horses"- are born). It might be a bubble in the Ethereal or, given its traditional "mind" associations [in the RW, not really D&D], the Astral...One Prime World's Plane of Dream is not/need not necessarily be attached to another world's plane of Dream, so, separate demi-planar bubbles.
Ravenloft, again, is one of these. you can tack it on anywhere you happen to be...but it doesn't
have to be tacked on unless you want to use it/plan to adventure there. Demi-plane bubble.