It still makes sense to ask what is the complexity of Many Worlds QM and how much probability does it contribute to QM, and what is the complexity of Collapse QM and how much probability does it contribute to QM.

You can of course introduce the universal prior over equivalent formulations of a given theory, and state which formulations weigh how much according to this prior, but I don't see in what way this is a natural structure to consider, and what questions it allows to understand better.