Reading through the spec, this seems like infrastructure that a couple of other specs are currently relying on, but one that could be potentially useful for future cases. (e.g. one can imagine a "cross-origin data worklet" that has access to cross-origin data and uses it to generate performance-related histograms in a secure way that doesn't leak any user-specific data)

Given that, I think it'd make sense to make this spec more agnostic to specs that rely on it. In order to do that, I think it'd make sense to move all the SharedStrorage/FLEDGE specific bits to their respective specifications, and only define the infrastructure (that can serve both cases) here.