1. Why not assign karma by running something like pagerank over the vote graph? I think giving overwhelming weight to high karma old-timers would make HN more like them, which would be an improvement, right?
2. What about assigning karma not by your comments, but by the responses to them?
I figure karma-from-replies would shift the conversation to "what should we be asking about this", whereas karma-from-comments incents "what can i say that the masses will like".
Given commenting has a higher work threshold than voting, it might be "manipulated" less. Gaming it would be more obvious. And subjectively, posts that are questions seem to lead to higher quality discussion (more genuine?). Maybe you'd have to put more work into getting users to not feed trolls and assholes, and ask/reply more to excellent comments. Not sure if practical...
Would love to hear anyone's thoughts on this.