Back in the email days, I used to try and get people to nest their email replies. But that was too much work or too complicated for most people.

Slack was awful for being single-threaded. Is it still ?!

X.com seems to be multi threaded but it is hard to see the threads. I find it unusable for discussions, and only use it as a read-only newsfeed. It would be vastly improved if one could easily follow discussion threads, as per your idea.