You beat me to it. Ive wanted this implemented since the old gen games. Ive always wondered why they havent added this yet. Like you said Bowden and Paterno wont coach forever so its pretty unrealistic to be in year 40 of my dynasty and BB and JoePa are still there coaching away.
Maybe have the real head coaches and a fake OC and DC(or the real ones if possible or just have ALL coaches fully editable) and those guys can get promoted, replaced, etc whatever.
I also think itd be cool if somehow the college coaches can get hired into madden...and vice versa, madden coaches can come down to the ncaa ranks. But i think this one may be really hard to do.