Yeah it's hard to say what the long-term future holds, but personally I think an Elvis park or a Beatles park would actually still do OK. Both are still recognized brand world-wide and still get a lot of play time if you listen to the right stations.
Plus you have to consider that Dolly's life and career made it further into to the digital age than either Elvis or the Beatles, so I feel like a lot more of this generation knows and understands her vs. some of those that came just before her. Plus all of her philanthropic endeavors have gained her some long lasting fame and recognition.
Also, DW really isn't that centered around Dolly. She has never turned it into an actual Dolly theme park. I feel like she is more of an added attraction or brand to an already huge and popular theme park. I think most of the customer base knows in various terms that Dollywood is an SDC with a Dolly museum.
So all-in-all, DW isn't going to change names within the next 25 years. 30-50 years from now? We'll just have to see.