For the record, I don't watch anime and I am largely unfamiliar with all but the most surface level examples of the medium, but I do see merch of Demon Slayer at Target or Walmart sometimes. I've heard people bring it up in passing, and I've seen enough people dressed as the girl with the green thing over her mouth to recognize it as Demon Slayer.
The example of Pumpkinhead is simply to correlate it with something that honestly, in year of our lord 2023, isn't a relevant IP in the slightest. Will people bring up Basketcase or Hobgoblins sometimes? Maybe, but I've honestly never seen references to properties like those outside of diehard Horror or movie buff fandom. No official merch even in a place like Spirit Halloween let alone Walmart, no convention presence in ones that I have been to, etc. It's not to say that any of these aren't worthwhile IP, I'm just saying that tossing the entire medium of anime out the speculation window feels weirdly abitrary when we are so willing to plead for our favorite toys to make it in despite them probably pushing ticket sales a negligible amount. Where's the Legacy post talking about the different audiences HHN reaches again? Some properties only serve audiences that are already guaranteed purchases.
Universal has been going after different audiences with HHN for a bit now. People thought Stranger Things wasn't Horror enough, that Billie or the Weeknd wouldn't work. Now Stranger Things 4, Dawn.FM, Lady Gaga are brought up every other post. It's weird until it's not. There is also an age factor to this, with some properties skewing older and some younger. I have also noticed that most ideas skewing younger (Billie, Weeknd, FNaF, Stranger Things) are pretty openly mocked on this board. Demon Slayer clearly has a much better shot than most other animated IP that are brought up frequently like Scooby Doo, or other localized television like Squid Game.
Are there larger anime properties than Demon Slayer? Sure. But once we have official confirmation that the Summer Walkthrough idea is underway we can start discussing if Dragon Ball, One Piece, Naruto, Jojo, and stuff that has really become ubiqutous in pop culture would be chosen instead. It's a horror event, and besides maybe Attack On Titan I couldn't name a bigger horror-adjacent anime.
Demon Slayer is on the spec map. I don't believe it is coming and I have zero strong opinions on the property itself, but I think to say it can't just because it's anime is just incorrect.
For emphasis, I'm going against the idea that it can't come to the event due to it being anime, not that it won't come to the event this year, which is a critical distinction. It most likely won't be represented this year, but it without a doubt has a reasonable chance of consideration.