That though, is merely a guess. Outside of the T2 Replacement, who say's it has to be a 4D attraction? To be perfectly blunt, I can see Trollseum be more of an exhibit, with it being more similar to Coraline to Kubo: A Lakia Experience (which premiered at USH last year with critical success) than I would see of a 4D attraction at Hollywood. And that I can see it being of the evolution of the Trolls IP, from the beginning of it's run to the DreamWorks film.
Keep in mind, this is mainly a guess on my part for Trollseum, and that I have no true insider knowledge on what is with Trollseum.