For me it looks like the use cases for Panel so far have been creating end products like dashboards and apps.
I see libraries of Panel Extensions as a natural, emerging use case as our use cases, code base and knowledge increases. The libraries can be private for just your work or shared across the community.
As the Panel Extensions use case is new (to anyone but Panel contributors) I think this use case is not fully supported in the current design of Panel. I’ve created a few issues on Github in this regard.
and there is new WebComponent pane that I need published some where (See PR on WebComponent) to more easily support Panel extensions with bidirectional communication.