I know it’s bike-shedding at this point but I really dislike slacks threads.

I would highly recommend looking at Zulip and telling me what you think. a good example of Zulip in action is the Rust communities Zulip instance.

rust-lang.zulipchat.com

I much prefer Zulip's thread model to Slack's (it it bolt-on and poorly done: threads have no titles, they get lost in history as there is no way to list threads, and they are optional so people only use them some times), but I prefer Slack's UI to Zulip: in Zulip everything feels a bit 'tight' and too close together. Also the big outline box for keyboard navigation is distracting to me.

Seems like an interesting study in developer-driven design: in Zulip the mental model is much better, but the appearance of the UI isn't as nice.

Zulip cannot be read without signing up. That's very annoying.

It is a feature that's currently being worked on actively. You can follow the work here: https://github.com/zulip/zulip/pull/16131

There is some ongoing work on threading https://github.com/vector-im/element-web/issues/2349

Apparently it's already in the protocol, just needs UI support from the clients. Not sure if they use Slack model though

There are two threads (heh) of work on threading in Matrix - one is label-based threading like Zulip: https://github.com/matrix-org/matrix-doc/pull/2326, which is implemented today in Synapse but isn't exposed by any(?) clients. The other is full HN/Reddit/Twitter/FB style threading, as per https://github.com/matrix-org/matrix-doc/pull/2836/files, which has been implemented at https://github.com/matrix-org/cerulean and if successful will get fast-tracked into Element. Quite what the UX will be is unclear, but it's unlikely to be Slack/MM/Gitter-style.

Oh thanks for the info! Even better, I'm not a big fan of Slack threads anyway :)