You don't have to sit out a year if you are transferring to a lower level 4 year school, but pretty sure you have to sit a year if you are transferring up from one. When I was at State a few years ago one of my roommates came from a D2 school and he had to sit out his first year.

If I'm mistaken, I'm all about your idea... Which makes me think its been thought of before and a rule put in place to prevent "poaching".