It's something I feel quite strongly about: chat should not be archived. There should be no backscroll; being not around when people are talking means not being part of that conversation. Chat messages have no value beyond the moment. Any chat implementation that assigns importance to messages beyond the current conversation is wrong.
For the rest... It was like peeking into an alien world. I've been maintaining an open source application since 2004, and I've had various day jobs, but managed to build it out into my day job the past couple of years. I've never had the startup itch :-) Just let me build up my userbase, my income stream and my contributor team, and I'm happy.
Persistent chat is one of the biggest values of Slack or Discord or Mattermost, and one of the big reasons I'll take it over IRC any day.
Persistent chat that you can join and read the backlog of is incredibly valuable. It becomes an asynchronous communication medium, rather than a synchronous one. And it's much richer and lower-friction than email.
Similarly, I'd disagree about friction, but I can see how that might be cultural/personal preference - none of the chat systems I've used provides good-enough tracking of "I still need to take care of this" compared to email clients with a few flags.
What's the value in removing this? I regularly look back to see what was discussed, it allows easier integration across timezones. I don't want to have to be around late for my American colleagues, or have to shift the conversation to large cc'd email. For chat I am involved in, why do you think I shouldn't be allowed a history of what I have talked about with people?
We must use chat very differently, because I don't understand this.
The number of times I've found answers to problems ("How do I X? Why can't I get Z to work with vagrant?" etc) by searching through Slack channels, or viewing pinned messages that explained something (or had a workaround/fix for a problem) is huge. This has been especially helpful when joining a team, where searching the archives can be the first step in finding answers.
A lot of what we chat about could safely be ephemeral, but there's a significant amount of company / team knowledge which can be searched (or pinned). The friction necessary to have people put answers in Confluence (or similar) is high enough that often the answers (or discussions around them) are either never written, or not updated later.