Licensing probably could work in this industry but it would be a tough nut to implement. For starters, as others have mentioned, with so much change happening, re-licensing would probably be needed, and of course that's a huge cost, a pain, and overhead as well. But then again, as I think about potential solutions, I am kind of coming up dry. Really need to mull on this some more.
It can just be a general aptitude test done in several popular languages of your choice with some level of customization based on what sort of programmer you want to be.
For all the change that happens, though, the fundamentals are still the same.
plenty of garbage lawyers passing bar exams, and law firms don't just check that you've passed the bar and hire you.
So, like certifications? Last I heard those are frowned upon in our industry.
Only because they are too easy, or for profit, or focused on using a given product or unimportant concepts.
We won't get an agreement about the scope of the certification or even what answers are right. Too much change, too much opinions, too little rigor/science.