I associate Dr. Pepper's flavoring with black cherry. I've never picked up on a prune juice taste. The only drink I liked that had prune juice in it was Ocean Spray's Cran-Prune. It's disappeared from store shelves decades ago, likely due to the stigma of prune juice. Even Mariani's, a hometown packer of dried fruit, primarily prunes back when this valley was the prune capital of the world and to a slightly lesser degree, apricots -- before silicon chips took over the economy -- now labels their dried prunes as plums.
If Ocean Spray revived Cran-Prune as Cran-Plum, they would probably sell a lot of it. Even though prunes are not considered plums (I still like them fresh and crisp when they can be found in stores), if a name change helps to revive availability in various forms, I'm all for it.