the pros (e.g., rookie/low A minors) back to college.  What you normally see is a few players who want the college experience and didn't get drafted highly enough going to college instead of the minors so that they can improve their draft stock - in other words, declining the initial or even subsequent draft offer in order to improve their draft stock by their senior year. 

But that was already true in the prior system.  I'm not aware of anyone cancelling their minor league contract to play in college insteady, but perhaps it has happened somewhere.  It seems like you'd be fully admitting you have no intention of going pro at that point, and just want to get the college experience.