I think that's an awesome idea. The only thing is I think you should re-evaluate your criteria/point system. The first 3 criteria, email address, BTT id and social media could potentially be used as padding because they're not enough to prove anything by themselves. So that if someone displays a score of 3, you still couldn't really trust him/her because the score could be based entirely on the first 3 criteria.
I think your minimum trust score should mean that you're able to identify the person in case he/she defaults. Moving up the trust ladder would then serve to reflect the dev's competence and ability to see the project through.