Reading the Context proposal one thing that sticks out to me is that it's a bit unclear what the purpose of the Context object is. It seems like it's used by a provider as a filter for contexts that it can supply. Assuming that's the case, wouldn't make the type of context being requested part of the event name instead?

ie, instead of "context-request" it becomes "context-request-theme" and a theme provider listens to that specific event rather than all context events.