@dominic I think the clearest example would be gossip or ebt, at least the who get's which feed(s) part. buuutt I guess this could also be a helper method inside the muxrpc session...?
Another example I had in mind, which I'm not so sure about anymore would be ssb-ws. Making the websock endpoint termination would be really trivial but handing of the calls to the rest of the system. I'm not sure how to rig that in but now I'm not so sure I'm holding this up right... It's kind of a a plugin in reverse.
but yea, this mostly concernse inter-peer plugins. Most of the app-plugins would be fine without this, I think.