[maxerickson]

I imagine a major reason cyclists don't require licenses is because it would cost a lot compared to the benefit it would confer.

You could push the cost onto cyclists that want the license of course.

In the US the "exam" that most drivers have taken is so stupidly easy that it doesn't really mean much that they earned their license. This is less true for the young people that have had to do more work to get a license, but they aren't the majority of drivers yet.