Stranger Things HAS to be at the event. I casually enjoy the show (never would have watched it if wasn't coming to HHN) and loved the first house, but after that loved a few individual rooms and character-specific scareactors, but the houses were pretty lacking.
But you cannot have a series, narratively driven by group of people maturing from childhood to adulthood, fighting the same evil entity over the course of a decade, finally beat the antagonist in the 5th season and be like, "Nah, we're good with just having 1-4." It just makes no sense not to have it. It's a cash cow for Universal in merch alone and just imagine the fanboys and fangirls going through the house and getting to the final scene with Vecna...just breaking out in cheers every time they go through.
Unless Netflix is suddenly refusing to play ball, I don't see any possible way it doesn't come to the event. Timing is less than ideal with the ending coming 9 months before the event starts, but still have to do it. Its an insult to both the fans and the show to not see it through at the event. It's like with all the talk of IT coming, image if they did "It: Part 1" (electing to not combine the two into a single house), it being a smash hit with consistently the longest lines all season long, and then deciding to never do Part 2. Doesn't make sense. When you think of it as, basically a TV Series, and say that the first 42 episodes were represented but the last 8 were ignored is crazy.
Don't get me wrong, I'd personally rather have something else take up 20% of the allotted IP houses, but it's gotta happen.