I'm tired of constant chatting. Slack encourages quick, stream-of-consciousness, short responses. Plus, it's hard to find past discussion, and it's hard to jump in after being gone for a few days (or, even a few hours). Threads are absolutely the answer. But, the defaults matter - Slack isn't encouraging threaded, long-form messages. Instead, it makes all messages feel urgent - and it makes the cost of sending a mess…
Zulip solves the problem you mention extremely well.
Self-hosted software has its benefits. But, it's inaccessible to a lot of groups. So, I'm intentionally building more of a managed product. Controlling the deployment end-to-end will allow setting up new features more easily such as inbound email parsing.