I actually did experience something not too long ago that made me think of this issue of single-IP themed areas, and coincidentally it hit me as I was going to see a film of a Disney-owned IP: the latest Captain America movie.
I'm not comic book buff, but I do enjoy a number of superhero stories, shows, and films (grew up on the Batman and Justice League cartoons from DC), so I usually head into DC and Marvel films at least having some awareness of characters and potential story arcs, maybe a direct reference here and there. For the most part I enjoyed Civil War, but something hit me as it went on; I hadn't seen each and every film in the Marvel cinematic universe, and it started to get to me that not only did I only have a tenuous grasp of some of the newer characters and some of the references the story made, but there was actually one or two characters who had roles in the film whom I absolutely did not recognize at all. Just had no clue who they were. It didn't ruin the movie, but given that I had seen both The First Avenger, plus the actual first Avengers movie, as well as Winter Soldier, I really didn't think this would be an issue for me heading into Civil War. Obviously this is part of the synergistic concept of getting us to see each and every movie they put out in the MCU, the "don't miss this or you'll be lost!" concept, but it still irked me a little.
Thinking about it later, I kind of made a mental connection between that and themed lands; so much of what makes a Disney theme park tick is cultural nostalgia, something that hits you at times without you even realizing it, though it occasionally might smack you in the face. There are a few IPs out there that nearly the entire public can feel some connection to like that, and who are so ubiquitous that they influence tons of other franchises...but they're very few and far between. You don't get the full impact with them without having some level of nostalgic familiarity with the source material; it can still be good, still be enjoyable, but that last ingredient isn't there if you're not engrossed and getting those subtle synapse firings to make some type of cultural connection. It's why broad concepts like "Adventureland" work; the idea of a tropical, "exotic" locale speaks to the vast bulk of Disney's potential audience, and the concept is general enough that Disney can try out all sorts of concepts within it, from a pun-laden boat ride through the rivers of the world to a room filled with singing birds and tiki figures, and yes, even to an attraction here or there based on a film that fits the bill of "adventure" (e.g. Indiana Jones).
When you go single IP, you really do limit yourself, and you set yourself up for obsolescence once the theme of the area isn't cool anymore. Star Wars might dodge this; it's been around since 1977 and here in 2016 people still get surprised when they hear a friend hasn't seen Episode IV. Jurassic Park in Universal could dodge this, as it's a property based on theme parks and the very general theme of "here be dinosaurs", which is a great hook in and of itself. Harry Potter might work long term because of how many generations its fandom encapsulates and how dense the fictional world of Potter is. Cars might be work long term in Disneyland because the theme of "America's desert highways" has some cultural nostalgia appeal, so maybe the land could be adapted if the actual Cars movie theming doesn't last long term.
Point is, I don't think it's impossible to pull off well, and there are some franchises it can work very well with long term, but you have to really weigh which ones can last, because frankly, I don't think most of them can. Maybe Avatarland will be great, but what if the new Avatar films don't do amazing business? You've already limited the area to Avatar themed attractions and ideas and won't want to spend a ton to renovate it so soon after opening.
