Today, you can implement IWSMInspector in order to add a new inspector for websocket messages. However, the code used to LoadInspectorsFromAssembly only looks for IWSMInspector if the inspector is also an IResponseInspector2.
This is overly limiting and a problem because, for instance, you might want to build an Inspector that can only look at WebSocketMessages and you don't want it to appear in the Inspectors tabset of regular HTTP(S) ResponseInspectors.