Great idea, but there's problems.
Few will go to the wiki page to start a discussion of a problem. People start problems in other forums, and then it may evolve into "fix the wiki." In order for it to work I think there'd have to be active forum moderators that moved threads to the wiki forum when the wiki needed resolving.
Secondly I think a forum about the wiki discourages edits. As I noted in the lets vote on changes thread, requiring to have votes in a forum and deal with critics and troll's is enough to prevent 90% of the people from even trying. In my experience forums get a lot of people who like to complain but not take action. Wiki editors need to be positive action takers. So the forum is not necessarily conductive to what the Wiki actually needs.
In my opinion, go for it. Be bold! If someone doesn't like your wiki edits, there's an undo button they can press. Every wiki page has a discussion tab already for this purpose, so no forum is needed.

