The problem with changing the artist of Rock n' Rollercoaster, is that there will never be a majority happy with the change. The novelty of speakers on a rollercoaster has passed, and it's time for a complete retheme away from music.
What I would personally like to see, is a retheme to a run-down part of town in 1940s L.A. to go with the classic Hollywood theme. Guests enter into a warehouse full of stolen goods before gangsters arrive and they escape out the back, boarding the coaster. At the point where it currently counts down before launching, recreate a scene like The Public Enemy from the Great Movie Ride, where a car pulls up and guests find themselves in the middle of a shootout. When the train launches, the theming can be adjusted accordingly to the 1940s theme.