hn is probably the worst place to implement such a system, since members already reserve their upboats like a jew hordes his shekels. At the same time, however, it's the perfect place to implement such a system, because elitism and self-importance are such mainstays to hn culture.
Anyways, I haven't browsed it in months, so I don't care. The only shame is that the monthly freelance threads are a good place to find decent paying work, and those threads will probably be rendered useless since employers typically won't have the karma necessary to see replies.