Speaking of #WebXDC: It is also used by one, two #Jabber clients now, but I'm not yet convinced, if I would want it.
It brings a large stack of web techology into the #chat client. Sure, in a very safe way, but it still adds complexity for devices without OS webview.
Useful features like shared TODO lists etc. can be implemented in #PEP or #PubSub, IMHO.
There is one application, I'ld like, however: https://webxdc.org/apps/#arcanecircle-livechat A chat in a chat! Does it use #XMPP by accident 🙂