Isn't that already the (desired) standard for upvotes, though? To promote high quality content, regardless of whether we agree with it nor not? I'm still not quite sure of the intended difference between them.
But if the upvote/downvote buttons have ended up being used as "I agree/disagree" buttons instead of "productive/unproductive discourse" buttons, what mechanism will stop the "endorse" button from also ultimately becoming an "I agree" button too?
I understand the desire to promote higher-quality discourse, but why not go with a less drastic method, like making the value of a user's upvote equal to their average karma, so people with better reputations on the site have a greater influence in sorting comments to the top of the page, but their endorsements aren't required in order for the comments to be seen in the first place?
I'm afraid that with the solution you're planning, it'll become extremely difficult for new users to establish themselves on HN, and HN will become an essentially closed community.
