I think with the salary cap for rookies, prospects would be idiots to return to school if they are ranked in the top 10, the difference in money just isn't worth the risk of injury in your senior season.
I believe it may not have a great impact this year but by next season, anybody who isn't a top end pick may well return to school to improve their salaries for the 1st 3 years in the NFL.
I think you will see many many holdouts in the coming years because of the rookie salary cap, many of which will continue into the season as the younger players attempt to get a better contract after their rookie seasons.
The full impact of the rookie salary cap is yet to be fully understood, but I think it could get real ugly by year 2 and fans will be wondering why they supported the idea. Add in the fact, that a lot of parents with kids who play skill positions, will direct their kids out of football and into better paying sports, and the NFL may well question their wisdom in the coming mess.
And proud of it!!!