Facebook and YouTube already do stuff like this: "too many people are just having fun clicking like on funny images instead of typing long comments, so let's increase the newsfeed and recommendation penetration of posts and videos with more comments... oh, shit, but now we are promoting flame wars as the best way to get more comments is to troll people".
While my policy might seem similar to theirs, were I in their shoes, I wouldn't be trying to promote content just for generating comments. Number of comments isn't a particularly useful measure for anything other than.. measuring how much discussion the content creates, it's no indication about the quality of that discussion.
