Plugins could include an additional meta header: "Context"
This would be a list of contexts for which the plugin should be loaded. For example:
Just to name a few. Obviously not all of these may be technically feasible, but we provide as many as we can. We could even support context negation, so you could just list the contexts where the plugin doesn't apply. On load, we figure out which plugins apply to the context, and only load those ones.