It's a tough problem.

Once some users have extra power to push content to the front-page, it will be abused. There will be attempts to gain that privilege in order to monetize, profit from or abuse it in some other way.

The only option along this path would probably be to keep the list of such users very tightly controlled and each vouched for individually.

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Another approach might be to ask random users (above certain karma threshold) rank new submissions. Once in a while stick a showhn post into their front page with up and down arrows, and mark it as a community service. Given HN volume it should be easy to get an average opinion in a matter of minutes.