So would it be correct to summarize zulip as real-time email?
I wonder what would have happened if they used the tech to build a chat application instead of an email-killer.
(2) It tried to be an all-in-one comm platform, and because of that it excelled in none of what it tried to do.
(3) Poor UI performance was the death sentence of it. If you can't use it fluently, it's not good for real-time. Poor UI design did not help, on top of that.
It was an interesting experiment, but not all experiments end up with a successful product. I hope the ideas will be unearthed at some moment and reused with a greater effect.
The UI is built for efficient real-time communication, but the underlying data model (the log, notifications, statuses, etc) allows for very easy async communication.
I think someone could make a great product by just adding IM-like UI features on top of an existing email backend. Email is pretty fast these days to work as mostly-instant communication.