I have a great idea for instant replay which I feel would be embraced and endorsed by most NFL stakeholders. How would I best suggest this rule to protect my copyright interests?

You want to copyright a rule? Guess you have to print your own rulebook then!

Hire a lawyer.

I think you've hit upon the reason the NFL can't/won't consider your idea. They're not going to want a process they don't "own."

Besides, Internet voting has already been done.