[Antoine Pitrou email@example.com]
... That's a complete strawman. python-ideas is a failure, and it would be as much of a failure with a non-threaded discussion system. ... Yes, but why? Because everyone really wants the governance discussions to succeed (and to succeed as soon as possible), so they make an extra effort to avoid derailing them. Such self-discipline doesn't prevail for the more usual python-dev discussions (let alone python-ideas which is its own universe). People are human beings, they get carried away, and I'm sure they will on Discourse too (unless they entirely refrain from posting because they can't stand the discussion system, that is).
This may be a clear demonstration of one way Discourse "works better": the "conversation" we're having here is really of little value to anyone, including to us. But because replies instantly show up in our inboxes, we're seemingly compelled to keep it going.
I don't have "mailing list mode" turned on for discuss.python.org, so there's been nothing nagging me to "reply or die" there. If I don't reply to something in my inbox almost at once, it will almost certainly scroll off the list of messages I can see on the first Gmail page within a day. Discourse has been more like a reasoned discussion than a hasty IRC chat room. Which, sure, may change.
In any case, I'm done with _this_ discussion now - have the last word, if you like :-)