Nothing is impossible, but it seems fair to say the NCAA will never implement a system of relegation and promotion in the FBS. There is too much money and power to lose, among the myriad other problems that stand in its way.
That doesn’t mean we can’t imagine an alternate universe in which college football functions like English soccer, where the worst team in each Power 5 conference (Premier League) is relegated and replaced by the top team from a Group of Five feeder conference (Football League Championship) at the end of each season.
The system would be geographically friendly (with an assist from Twitter user @OffHiatusBBC): The Sun Belt feeds the SEC, the American feeds the ACC, the MAC feeds the Big Ten, the Mountain West feeds the Pac-12 and Conference USA feeds the Big 12.