This is (kind of) what Google Wave advertised itself as being a solution for. Comments on the document appear inline in the document itself...

Shared with a small, trusted community, you can get by with a Google Doc or wiki page, but neither are really properly suited to this task.

I think, if Google Docs would add a feature where people can tag comments to different page elements but not actually change the page itself, we'd be there. The curator/author would then be responsible for integrating comments and suggestions.