As it stands currently, there really is no definitive "line", its more like a jagged scribble with 1,000 different rules. And there is also no enforcement, really.
I'm not concerned with everyone following the rules, because people don't follow the rules now.
As for where we draw the line, I don't know. Some of the rules in place are ridiculous (players can't sell their own 'memorabilia', players can't have jobs, etc.), so perhaps just doing away with those rules would help. I'd also be agreeable to men's football and basketball players getting some type of annual payment. If people were aghast with this, you could say that only players who are academically eligible will be able to receive the annual payment.