We can thus safely assume a nonlame set of articles, and we also (so far at least) assume nonlame voters. And if you only have nonlame voters voting on nonlame articles, upvotes should be enough to pick the winners.
However, all of this is missing the main point: for a site to be popular (lots of eye balls) and be able to sell itself to a large media company for a large sum of cash, it needs to appeal to more than a small, coherent community. Reddit changed because their founders wanted to cash out. HN isn't changing because you have no (apparent) goal of cashing out, and are thus willing to keep HN as it is.