This idea also struck my mind but later i realized that if we add comments to the forum, what will be the difference between blogs and forum ;) so if you want forum with comments simply rename blogs to forum from language.
Yep, like I said above - depends on the kind of content module. Also, main poster would have to explicitly "invite" people to post in forum and set out the rules. I little tedious and not very flow-ey. :)