Really? If anything, I'd gotten the exact opposite sense from it. I mean, they want to make sure the return to the Great Wheel cosmology doesn't automatically enforce Planescape on DMs who don't like that "Hey, you got your Planescape in my Forgotten Realms!" "Hey, you got your Forgotten Realms in my Planescape!" crossover that was so common in the 2E days, but from what we've been hearing from Legends & Lore, these live tweets and especially Wyatt's Wandering Monsters column, Planescape sounds like a shoo-in.
EDIT: I fear you're right about Ravenloft, though. It sounds like they want to carve out a niche for it for DMs who want to run it, but they're not necessarily going to produce any material for it, other than reprints of the old stuff.