Interesting. So perhaps a non-profit could start a grass-roots crowdaction campaign for all researchers in a field to switch to open-access overnight, and use US contract law to enforce compliance (in the US) if the threshold is reached?

There could be some penalty that researchers agree to pay if they renege on the agreement, and that penalty could be contractual. The non-profit could collect donations for marketing, and enforce the transition through legal action (if needed). Any proceeds could go to funding the next research field's crowdaction.