After reading through all the posts in this thread, I want to touch on a few things..
1. The idea of photo-ops at each house is pure gold. Almost every IP that comes in already has some sort of cool visual that the general public is aware of. Let's use Stranger Things as the example. Imagine a Castle Byers. Star Court Mall, etc. photo op? You could staff it with or without an actor, and it would still be effective. You know whats better than paying for advertising? Free advertising! Posting about your vacation or night out is more or less what platforms like Instagram have become all about. You can search right now on Instagram and see thousands of posts from the Klowns photo op.
...and you know who really has a strong pull on social media? The youth. Like it or not, things that go viral have a tendency to do so with early adopters (in this case tweens/teens/young adults) first, then later on they reach the laggards (call it post college and older). These photo ops can become synonymous with the event much like the Purple Wall became to WDW. We see know how WDW is starting to actually market to young crowds with these photo op walls in real commercials, so regardless of how odd you think that may be, Universal would be crazy to not dip their toes into that same ideology.
2. I experienced that weird hangout thing at Mel's at HHN 28, and yeah it's different, but I don't believe in putting an age restriction on solo visitors, or at least not one that's as high as 17 like some people mentioned. You could probably sell me on 12 years old to come in alone, but if you start going older than that then I feel like you are alienating a portion of your future guests. If I lived in the area as a kid, I'd have wanted to go all the time when I was in my teens. Yeah my parents might take me once or twice, but after that they probably wouldn't want to go as frequently. The ones who are bad, can get kicked out through standard security procedures, but those who play by the rules should be allowed to share in the fun with all of us.
Even from a business perspective, I don't think it makes sense. Sure Timmy and Sarah might not buy a lot at 14 years old, but if they become invested in the event, then by the time they get to their 4th-5th HHN, and they are now college-aged with some sort of income, they'll be bringing more friends with them, starting to buy merch and food, and by the time they turn 21, they'll be hitting Finn's and Duff Gardens for $10 drinks with the rest of us. If you kick them out now, they'll find other events to visit, or other passions, and that's potential revenue that will be harder to win back years down the road.
3. If there's an anniversary house of some sort, I think it'd be cool to run it under the guise of a Slaughter Sinema 2.0 kinda deal. Instead of B-Movies, you walk into the (icon?) main character's highlight reel of their favorite house moments. Scarecrow and Yeti feel like locks, but if Scarecrow got its own sequel of a house, then that sounds like it would be a fun idea as well.