> I would like to see an alternate history where Slack is built entirely on XMPP, with plenty of extensions to support all the customisations for every feature they have now.
Writing and maintaining a protocol and a client and a server is certainly harder than just having a private proprietary protocol.
For what it is worth it seems XMPP is cherry picking features proven in proprietary protocols and standardizing them. It seems like there is a small set of such critical features as can be seen by supported XEPs in modern clients (https://dino.im/https://conversations.im/).
Writing and maintaining a protocol and a client and a server is certainly harder than just having a private proprietary protocol.
For what it is worth it seems XMPP is cherry picking features proven in proprietary protocols and standardizing them. It seems like there is a small set of such critical features as can be seen by supported XEPs in modern clients (https://dino.im/ https://conversations.im/).