That's going to be tough to get backing for, and should be. With no meaningful labor coordination, the only way that happens is for a few unaccountable people get together and dream up their idea of what that certification looks like, then do a lot of politics to stick everyone else with it.
Sure, maybe you open-source the initial development, but you can't open-source the politics because nobody can have a sensible conversation with a million people working at at least partial cross purposes, and so when you're doing the politics you make a lot of compromises that nobody gets a say in.
Best case you fail, worst case you succeed and everyone is stuck with the result, which inevitably favors employers because why do they even participate if they don't get something at least a little more like a buyer's market out of it?
So nobody with any experience, maybe even nobody with any common sense, participates in whatever process you have from the design side, because all that does is waste time lending legitimacy to something that's guaranteed to be a bad deal for labor. You haven't even sold me on it!
Of course, if you have buy-in and trust from a sizable and valuable labor base first, all this changes. But that means a tangible history of success as part of the leadership of a union, and you've already ruled that out. What you're proposing would be more like a guild, which is actually a model that can work when the people who run it also monopolize the local industry and can exclude anyone who doesn't meet their standards - including preventing other business owners from defecting and hiring skilled upstarts who the guild won't accept for inevitable and again political reasons. Management in this industry isn't that coordinated either, and can't be without being a lot more oligopolistic than it already is.
Maybe in a few decades. Right now I don't see it.