Being able to setup your own server is a benefit, not a negative. Much like twitter it seems to be another regressions from an open internet to corporate control.
The only positive I can see is rich text, but that has extremely limited value in a chat program. History is nice too but IME too painful to use (scroll, load, scroll, load, scroll, load) to be of any practical benefit.
Slack has search for history, which is huge. No more "eh we talked about it".
Onprem is great. But it's a hindrance for quick adoption.
I'd love if an open system would win. I've no love for Slack and don't use it. (Have used hipchat; what a UI mess like all of their products.) But I guess no one stepped up with an IRC-based platform that could compete.
For functionality like that it sounds like a mailing list would fit the use case better.
> Onprem is great. But it's a hindrance for quick adoption.
It's not either/or. Think of git, you can use a hosted server or a private one. The ability to host your own server doesn't hinder anyone.
Then you're looking at an email with the visual noise of recipients and whitespace and signatures, and if the UI is really bad (mailing list websites, for example), every message is viewed in isolation without the responses.