My proposal outline (simpelst):
* Have a "Post comment" button
* That adds a comment you write in a blank edit box, attaches your
signature, date, etc.
* It also inserts some tag in front, to keep track of "who answered what
to whom"
* All that is added/inserted into the talk page
* The talk page is still wiki-editable
* Every comment contains a "Reply"-link (part of said tag) which opens
an edit box (see above).
We'd be adding some tree-like structure without losing the wiki way.
Magnus
P.S.: I'm too busy to code something like that in the next few weeks ;-)