We should be updating the topic for the next release in the next month or so to better reflect our high level plans for the next release of Discourse as a whole, but we haven’t been maintaining a public roadmap for chat or other particular features.
You may be able to make some sense of what’s getting attention by lurking on the discourse/discourse repo and the chat tag here.
Happy to share more informally about what our current priorities are for chat in a separate topic.