I absolutely agree. The “Social Share” plugin mentioned above is not usable on Discourse instances with login control (privacy!). The discussions we had about some technical integration between the proprietary Discourse chat functionality and the federated MATRIX chat protocol also had no result yet (see Matrix protocol for chat and my last comment at Matrix protocol for chat - #69 by Thomas_Rother).
I have the impression that there is not much interest among the Discourse core team for the integration of federated information flows.