Thanks, that’s helpful context! From my perspective I think the Discord approach here is arguably a better one in that it potentially avoids the need for a setting at all. It flexibly supports both approaches. I suppose if you want to empower admins to force all replies to be threads then it’s still necessary (and I’m curious if you have user data that suggests this specifically was desired), but if you allowed for both threads and in-line replies then both use cases are served to at least a reasonable degree. I can’t think of a Discord community I’m in where people not using threading and only replying in-line has been an issue. And the existing Discord “hinting” to create threads when replies get to a certain number helps to solve that, too.
In the case of Discourse, as I mentioned before, the admin also has the ability to move messages, which could now be into a thread. Although I wouldn’t want to put more burden on admins to manage such things, if the “move into thread” function were well-supported in terms of e.g. auto-selecting all replies (i.e it was very quick and easy to create a thread after the fact), and if sufficient Trust Level users could perform a Thread-creation action from existing in-line replies, it feels to me like that would be within the Discourse philosophy (empowered, trusted users helping with maintenance) and would well support most needs around thread vs. in-line. That’s my 2+ cents FWIW. 