What would happen if you make reddit/HN submission score = to # of people who comment on it?

Controversial and flamey topics would shoot to the top and more considered, but denser topics would languish.

I think it'd definitely be a good idea to make submission upvotes not count towards karma, or be counted separately.

It might be useful as one factor in a complicated score function. You need a factor that diminishes the score over time, too, so it can't be quite as simple as you describe. In general it seems like you don't want a comment saying "This is as insulting as it is factually incorrect" to count as an up-vote.

More people would comment just for the sake of commenting. Comment quality would suffer.

But poor comments would be downvoted.

Perhaps a more interesting solution: Make article points equal the total number of points in comments. (Naturally that's not a perfect solution either.)

It's a good idea but it's not practical. It won't make a proper measure.

Sometimes I make 3 or 4 comments on a submission that I wish I could down-vote it.