I could see that working, with the right community and moderators, especially if the choice were presented not in terms of simply flat-vs-nested, but "what is the goal of this discussion?" Those for informing and airing possibilities might have certain titling, features, and moderation (including nesting)... while those for hammering out some common experience/decision would have other titling, features, and moderation (including flatness).

(Remembering, as always, that it's not exclusively a goal for software design to solve, but also and probably primarily up to the participating people and their behavior... who can and do bend any offerings from the designers/coders to their own ends.)