It would require that group to agree on what being a "good" developer meant, but there could be more than one and if you don't agree with this one you could form your own. Maybe one requires people to be able to write testable code and be able to label design patterns, and another expects pure functional programming, and another expects deep security expertise, and companies could know which of those they are looking for and inquire appropriately.

We have this a little bit with employers like Pivotal or ThoughtWorks, that have such strong learning cultures you can be sure that if someone spent five years there they know their stuff. But we could have a version where workers were willing to endorse each other, rather than relying on a specific for-profit company.

It is, like all certifications, only as valuable as the least-competent person who holds it. But the informal versions of this are pretty powerful.