Even as far back as the 2nd edition boxed set Ravenloft has had a Cthulhu Mythos domain.
Ravenloft is very meta - it represents D&D’s ravenous assimilation of anything in the horror genre.
Ravenloft is a brand. It means “any horror themed D&D”. It’s long since passed being a setting.
But it’s the players who never understood that Ravenloft started out as movie parody. Which was then converted into a World of Darkness competitor, which was what the business needed at that time.
I seem to recall Deities & Demigods made them lawful neutral. That might be my memory playing tricks though. I used to have the original book, but I lost it decades ago. I couldn’t find an image of the original stat block on the net.
And considerably shorter than originally planned.
As I said previously, I think Perkins was lead on this project when he was pulled off everything else to help finish the 5.5 rules in time for the anniversary. So it was probably sitting around for a while waiting for someone to take it over...
The art is pretty unmistakable. And both Cthulhu and the Great Race have D&D history as both where in the original Deities & Demigods.
So now the copywrite is gone they (and probably more Lovecraft monsters) are being put back into the game.
Forge of the Artificer has plenty of new content despite being a small book. Bastions, airships, three campaign outlines…
I don’t think the new Ravenloft book will have significant repetition beyond things being updated mechanically. I’m pretty sure new campaign outlines have already been...
Bebble & Grime box set probably contains both Arcane books.
Note: this is pretty much equivalent to how the did the Spelljammer and Planescape boxed sets, only without a slipcase.