FWIW we have been seeing a lot of larger communities that previously were deadset on Slack because "everyone knows it" importing their data from Slack in the last few months.

Part of the reason is that Zulip's topics make it a lot easier for a part-time participant to use their limited time well (E.g. skimming or reading the conversations in most relevant to them in batch a few times a week). The Slack/Discord/IRC/etc. data model limits how effectively one can participate and benefit from a high-traffic organization without constantly watching it (and being in the organization's dominant time zone!).

More on the inclusivity issues with synchronous chat here:

https://zulip.com/for/open-source/

Man, do I ever miss chat services and chat clients not being so tightly coupled to one another.