"I'm open to more feedback on whether more people think an optional exam would be useful; but my first impression is that this may be one of those ideas that are good in theory but awfully hard to implement in practice."
I know people (not working on a '51 - thus not members here) that can pass any relevant exam with flying colors and stll not make anything work. While passing an exam might show knowledge, it show nothing about the ability to apply that knowledge.
If someone pass the exam and thus appear qualified, does that mean that their "tested and proven" circuit for RS232 without a MAX232(equivalent) now is a correct answer.

I fear that a "passed the exam" qualification may confuse the issue of quality of answers more than help it.

One man's opinion

Erik