XMPP is more than promising, its proven.<p>The major messaging (and notification, if you believe the rumours) networks are all based on xmpp.<p>The issues are basically: big vendors want lock-in so they disable federation and spam. I remember seeing an XEP that aimed to solve the spam issue for federated xmpp.
XMPP - Didn't use it in a long time. OTR wasn't a good experience.<p>Matrix - Works well, but UX is too techy for my non technical friends.<p>IRCv3 - never tried.<p>Currently, I am using Tox P2P, so far it's working best.<p>I am looking for a web client because native clients don't provide me Telegram like feel.<p>So, if I find some time, I'll be writing my own web front end.<p>I am also looking to hire people to work on my Tox web p2p frontend.