I understand your idea, but I think I would phrase it differently. Instead of gatekeeping the application, just make it part of the application process. Our application says something about we will consider grades, attendance, and effort when assigning leadership roles. We do not assign specific point values to any of those things.

Like Mr. Dude below, we started with the Scott Lang application document. I have modified it quite a bit over the years, but it's still an intense process. We do several sessions to teach the kids the skills they need and help them build their application package. Kids who aren't willing and able to do the application process also won't be willing or able to handle the responsibility of student leadership.

I also make it clear that playing ability is only one part of what we consider. We have several leadership roles that do not require the student to be good at their instrument. Some of my best "equipment manager" and "librarian" kids have been 4th band seniors who didn't know their left from right and could barely play a Bb scale, but were hard workers who wanted to do their part to help the band succeed. I've also seen kids really step up their game after taking on a leadership role, and suddenly they're practicing more and moving up.