 Quantum probabilities here would not be descriptive of which Everett branch is actual, since they all are. Rather, quantum probabilities would presumably be descriptive of the structure of the branch indexical perhaps somewhat as temporal duration is descriptive of the time indexical. While it is unclear, at least on a standard account of rational choice, why an agent should care to have such probabilities inform her decisions, it is not impossible that one might formulate a compelling story, perhaps akin to how temporal facts may affect an agent’s preferences. (See  relational quantum mechanics  for a further discussion of such approaches.)