If you say Doom: Dark Ages can't appear in Ravenloft some player will answer "Hold my beer!".
Mr.Squid was "invited" by the dark powers to become the "natural enemy" of the cult o Tharizdum. Its torment is suffering horrible nightmares where it is defeated by the doom slayer, Chuck Norris or even the Chapulin Colorado summoning the Rose of Guadalupe. And plot twist! Vecna has got a secret plan to use it with the intention to cause serious troubles to the Dark Powers.
Masque of the Red Earth was practically a Ravenloft spin-off but I don't advice adventures in the real Earth because some historical episodes may be potentially controversial, for example
the 1822 "Black Christmas" in the city of Pasto during the Hispanoamerican indepence war, the horrible 1649 massacres in Drogheda and Wesford by Cromwell's troops, or the "aceifas"(raids) by the warlod Almanzor against Spanish Christians (siege of Barcelona in 985), or the 614 Sasanian conquest of Jerusalem. The publishers with enough self-control and self-censorship can avoid possible controversies but these can't stop the possible homemade content by some players.
I don't advice an official update of the Masque of the Red Death by WotC because this could be relatively risky (if it is published in DMGuild by a 3PP then it is not our business) or to use our real world for our own D&D stories. Let's imagine an alternate timeline where Mary Tudor and Philip II of Spain conceive a daughter who becomes Queen of England. Some players would present this alternate timeline as a utopia, and others as a dystopia. Do you understand what I mean? And this could be worse if some player wants to add the "mythology" based in conspirancy theories about reptilians aliens using secret lodges to rule the world (althought this doesn't mean this player believed them to be true in the real life).
If you want to play in the Victorian age I warn you about the 1858 great stink of the Thames, the air in London was unbreathable on foggy days when the fog mixed with the smoke from so many chimneys and the crinoline, a popular 19th-century, voluminous underskirt made of flammable materials like cotton, caused an estimated 3,000 fire-related deaths between 1850 and 1860 (among the victims two Oscar Wilde's half-sisters).
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My theory is WotC should create a fantasy version of "Gothic Earth", among other reasons to can add all the fantasy D&D species, something like New Capena in the Victorian Age. Why not a mixture of Victorian age and a magitek version of 70s urban thrillers? Something like British 70s teleseries but with more fantasy.
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I don't want to play cosmic horror in the same way lots of Lovecraft fans. I don't want the nihilistic and hopeless speech the humanity is only dust in the middle of cosmos. I want stories of people who, although not perfect, try to create a better future for the next generations and who sincerely care about respect for human dignity, and where monsters and evil people cannot go unpunished so easily. In my stories I want space for the hope.
I don't mind the canon. I would rather stories style "Resident Evil 4" or "Evil Within" where there are horrible monsters but the main characters have got enough opportunities to survive and save the day.
"Sandy Peterson' Chulthu Mythos" show monster-stats for those "Lovecraftian lords" and I don't remember complains about this.
Have we forgotten the official Chulthu d20 in the 3e age?
* How would be a brainstealer dragonborn? Yes it sounds very weird and creepy.
* 3.5 Lord of Madness: book of aberrations had got some monsters that should be updated to 5e
