Get plugin corresponding to return values when calling hook

Perhaps this is already possible, and I am just missing something, but is it possible to determine which plugin returned each value from a hook call? This would be valuable information for providing error messages and the like in situations where one and only one plugin should return a value under certain circumstances. Being able to report which plugins returned which values would be nice. Perhaps something like an alternative hook calling mechanism, which would return a dictionary (keyed on plugin namespace), rather than a list?

Start by reviewing the existing hook-calling API and how plugin namespaces are represented. Define how a call would associate each returned value with its plugin, including the error-reporting use case, and verify that the proposed behavior fits the current plugin system.