I think the highest priority is to make it possible for OWAs to fit into
the current application, so that we can enable non-breaking innovation, and
provide a gentle path from the current code to whatever new evolves. So I
think that discussing global nav is a topic for another time. 
Tangent: In fact the app framework supports the general idea of extension point, and things that connect to it, so we could add jump navigation within that UI as an incremental step, without having every single OWA necessarily show up there. (E.g. we probably want to go in the direction of moving some of what’s currently in the uiframework-based UI Commons module into an OWA of shared UI components, that isn’t actually an app of its own.)
I’m suggesting a server-side, Java Listener and Observer pattern, yes. E.g. App Framework would register an OpenWebAppListener.