IMO this is perfect for a chat to handle, rather than the forum. Treat each message as its own post, attached to a single “thread” (the chat channel); display each chat channel in the forum as a thread in a special type of forum category that handles chats; allow users to post replies to any given message using Discourse’s forum post editor; allow users to post replies to any normal forum post using the chat as well, converting the post into a chat message upon their doing so. The chatlog can be displayed in a separate feed: this would provide a powerful discovery and curation mechanism for the forum, where users can resurface and open up discussions around a notable thread or post without having to commit to writing a full response. It would be something like Zulip without the counterintuitive UX.
There’s no fundamental difference between a forum and a chat, despite what the oldschool, chats vs forums people think. Actually, forums (cf. social media feeds) are closer to chats than they are to feeds: there’s very little that the users can do to sort and surface content; posts are inflexibly attached to threads and can’t be conveniently consumed out of context, even though the OP in a thread is seldom the most informative post of the thread (exceptions prove the rule: social bookmarking, tech support, work/project forums work much better); threads discourage branching out into new conversational contexts. Feeds strongly encourage interacting with content in a less linear way, so that you can dip in and out of conversations with many other people participating simultaneously.
Also, all else being equal, “shallow” content is better than “deep” content.
We have effective search engines and other discovery mechanisms that help us find good content based on clues. If I want to learn deeply about a topic, I can usually do that by finding and reading the manual. When a post or a video doesn’t get to the point right away or rambles on about some irrelevant or outdated material, that’s simply offensive to the viewer/reader. A platform should be designed to pressure users not to waste each other’s time, or at least allow other users to fully filter these out (e.g. blocking). When people can’t filter out low quality content, a platform becomes extremely fragile, and usually becomes worse instead of better as more people participate. That’s precisely the problem that Facebook is facing, and also why chats, short form videos, and subscription-based publishing platforms are ascendant.