Not every attraction has to be Potter-caliber IP. There are only a few IPs of that scale, and the majority of them are already represented in theme parks. Outside of Lord of the Rings, James Bond, and maybe Mission: Impossible, there's not much left out there for major film franchises.
Sure, you need a major IP or two for approval, but everything else can be a supporting role.
Thinking ahead of USF's future... what IP replaces Supercharged if not Ghostbusters or BTTF? Godzilla? Can't imagine we stick with Fallon long-term, what IP eventually replaces it? Can't imagine USF stays in its current condition for long.
I think Disneyland has done a masterful job at blending legacy & new IPs within the park. The park would have lost its charm if they had replaced Peter Pan, Mr. Toad, etc., but would have also lacked appeal with modern audiences if it weren't for Indiana Jones and Star Tours.