I struggle with this question. The editor plays a valuable role and it's not hard to swallow the argument that editors make science better, they're the front line filter. Employing them full time is a core value that the current system provides. I'm wary (but not close minded) to the idea that volunteer orgs could scale to the top echelons of scientific publication, which require a lot of filtering. Perhaps if we look to the conference paper model where funding primarily comes from the conference? The conference brings benefits beyond publishing. In that model publishing equates to financial discount or free entrance to the conference, so it flips the equation.