Why not just use XMPP? Yes, everyone hates XML, but the protocol is well designed, has sustainable funding (via the IETF and XSF), and there's lots of experience out there, and it's flexible enough to develop services like Slack on top of.
https://signal.org/blog/the-ecosystem-is-moving/
"XMPP is an example of a federated protocol that advertises itself as a “living standard.” Despite its capacity for protocol “extensions,” however, it’s undeniable that XMPP still largely resembles a synchronous protocol with limited support for rich media, which can’t realistically be deployed on mobile devices. If XMPP is so extensible, why haven’t those extensions quickly brought it up to speed with the modern world?
Like any federated protocol, extensions don’t mean much unless everyone applies them, and that’s an almost impossible task in a truly federated landscape. What we have instead is a complicated morass of XEPs that aren’t consistently applied anywhere. The implications of that are severe, because someone’s choice to use an XMPP client or server that doesn’t support video or some other arbitrary feature doesn’t only affect them, it affects everyone who tries to communicate with them. It creates a climate of uncertainty, never knowing whether things will work or not. In the consumer space, fractured client support is often worse than no client support at all, because consistency is incredibly important for creating a compelling user experience."
But I do tend to agree in general that we need fewer features and less complexity and to push more for basic profiles that everything should implement and that have a clear compliance label.
Now we have uncertainty around which networks people use, which devices they use them on, and which features each network supports.
You cannot just tell people "go choose any XMPP client, and it will work fine". Instead, it is more like "get XMPP client, but make sure it supports XEP-1111, XEP-2222 and XEP-3333". And if you have multiple platforms (Android, iOS, Win, Linux), let's hope you can find a client for each.
For example, I used to use Mcabber with HipChat at work. Mcabber doesn't support even basic modern XMPP things (history, for example), but it was plenty good enough for me to chat with my coworkers.
For your work: Are you connecting Mcabber to HipChat server? Do you use native HipChat client as well?