Another idea: Developer A posts there idea, and utilizes their social network to get feedback. Developer A's social network looks at Developer A's project, th

Another idea: Developer A posts there idea, and utilizes their social network to get feedback. Developer A's social network looks at Developer A's project, then comments etc. then is forwarded to Developer B's project. You will lose a lot of conversions between A and B, but it would add value to have completely outside people evaluating ideas and signing up for the email list. You could create a system where the more people come through a link created by developer A, the more referrals they get. That would incentivize developer A to not be a free rider.