What it's coming to, could be as soon as any player establishes himself as a surefire top 1-2-3 round draft pick, just quit then, as long as your eligibility for the NFL draft is not too far away.
I wouldn't quit before the end of my sophomore year, because IMO, more than one year of not playing, would make you rusty. But if you're entering your junior year, and next spring is your 1st eligibility for the NFL draft, then just hire an agent and trainer and QUIT and go work out somewhere. If you're just into the pure logic of it, and it's only about money. Then be logical.
It sounds like a lot of fans here are advocating that too.
Then again, I'm not sure if this would work for everyone, as long as you don't get lazy and get out of shape in the time off, some people need and thrive on the team dynamic to be motivated IMO.