Mailing lists are intended for whatever people intend them for.
I'm suggesting we split our current one into a version that continues to be a relatively open dialog ("wikien-open") and one that is heavily edited by volunteer moderators ("wikien-forum"). Some threads would be purely in the edited list. Interesting threads on the open list (or wherever) could be summed up or excerpted to the edited list.
I don't think a mailing list is the best way to hold such discussions, although I'm not sure of a better way. To be honest, I can't see the basic concept working, for the reasons I gave.
How it actually develops would be determined by moderator experimentation and reader feedback, and I'm pretty open to what that would be. The flavor I'd personally aim for is something between a moderated panel discussion and a well-edited interview.
Both those have a key feature - the people talking are preselected by some criteria (basically, that they have an interesting viewpoint). You're never going to get that kind of flavour with a public mailing list, even with heavy moderation. People watch panel discussions and read interviews because they think the people involved might be interesting. The same can't really be said for a public mailing list. Panel discussions and interviews are done for the benefit of spectators, mailing lists exist (in most cases) for the benefit of participants.
That said, inviting a few interesting people from inside and outside the enwiki community to take part in a panel discussion on an interesting subject would be quite good fun. It would probably work best on IRC (with published transcripts), rather than a mailing list, though.
My theory here is that many people are interested in the results of discussions on this list, but very few care to read the long arguments, the tit-for-tat replies, or the seven thousandth post on some issue that we will never settle. So we take turns editing that out.
Probably true. I'd say the solution is summaries posted on wiki of recent discussions - perhaps as a column in Signpost.
If you have an improvement or an alternate proposal, please bring it up. As Jussi-Ville Heiskanen pointed out, constructive comments are a lot more useful than purely negative ones.
Purely negative comments can still be constructive, as long as they point out specific problems and explain why they are problems. Requiring people to have a solution before they can point out a problem just means it takes longer to recognise problems.