Earlier quoted context omitted.
A set of RFCs isn't really in the same ballpark of the same planet of the same local galactic group as a mature product that I can go sign up for and be using in under a minute. Maybe in a few years. I say maybe , because XMPP is an IETF RFC, and frankly, it sucks.
What do you not like about the protocol? Like everything, it has its warts, but having worked on a few more-or-less proprietary protocols XMPP is much better designed and thought out than most of them. The community has had a lot of time to address some of its flaws whereas Slack, Stride, et al. tend to reinvent the same problems XMPP solved 20 years ago.
XMPP is a well-thought-out protocol, and a lot of the XEPs are great features. The problem I always had with XMPP is that XEP support is unequally distributed among clients, and the fragmentation really undermines the amount of cool features XMPP has to offer. As a (made-up) example, Psi+ might support video calls, but not server-side history, and Pidgin only supports server-side history, and Adium is the only one that supports Service Discovery...if I want both, I have to pick a client, and possibly have to use two clients signed in with different resources.
As a possible solution, we could have a "logo program" for XMPP, where a core set of XEPs are required to call yourself an XMPP client (this is the case already IIRC), and you get rights to call yourself "supporting XMPP-Enhanced" if you support these other XEPs, and "supporting XMPP-Full" if you support all of these XEPs. Something like that might work, but you'd have to have a way to actually drive development toward these features.