Better posters could do this themselves (at least for new threads), but its the people who don't care much about the quality of their posts that need it the most.
I think the challenge is that it'll only work if there is a high enough density of sophisticated participants that can understand that a reviewers role isn't to agree or not, but to help make the time spend reading it by all the other readers as well spent as it can be. But where it could work, it could be a big improvement. -- think of all the posts that the author would skip when someone just points them to where it was discussed before.