If this is the intention, then I'm baffled at how you intend your product to be used. Your advertisement of Zulip is completely at odds with... its fundamental principle? What I mean is, your website says "Zulip combines the immediacy of real-time chat with an email threading model", but it seems you're explicitly designing away the immediacy and requiring people to spend significant time thinking about what to type and clicking around to find the appropriate thread to reply to, just like with email. It can't function as a team chat system if it doesn't facilitate instant messaging -- "chat" systems are designed pretty much by definition to allow instant communication. (Like what "chatting" meant, before computers were around.)
What you really seem to have is a shared-inbox email service -- kind of like a mailing list, but in a shared workspace, which would produce something that's more close to the exact opposite of your description... something like: "Zulip combines the deferred/asynchronous model of email with the shared-inbox nature of a mailing list".
So here's my question: what do you expect teams to do when they actually need instant communication with the rest of the team? Do you expect them to have another (actual) chat system in parallel for that, or do you intend a model where you intentionally insert obstacles to make that viable somehow? I'm not talking about stuff you'd put in a email, so I'm not talking about something like "Let's discuss item 2 on the design doc. I think it would be better to approach the problem by doing X, then Y, then Z. This benefits us because Y helps us with Z and [blah blah]." I'm talking about stuff where there is something urgent going on and immediacy is the #1 priority, like "can s/b urgently cover me here I gotta run" or "what's up w/ the projector in C13?? I have a meeting" or "who's covering the slot rn? s/b's waiting" -- you know, the day-to-day stuff where the extra 10 seconds finding the right topic to reply to and the extra O(minutes) trying to articulate an eloquent email-like message for your team is going to tick everyone off (especially outside clients etc.) rather than please anyone. This kind of immediate communication is what teams need instant messaging systems like Slack for -- if your software is explicitly designed to discourage it, what do you imagine continuing to fulfill this need after teams switch to Zulip -- another parallel Slack?