I guess Kirk just really, really, really enjoys coaching because I can't think of any reasonable milestone he has left to achieve.
Sure it would be nice to win an outright Big Ten championship, make it into the playoffs and win a national title, but let's be realistic. In the new Big Ten, Kirk's ceiling is probably a 4th place finish and then make it to the quarterfinals (final 8) of the CFP
As far as overall wins, Kirk is not going to catch Paterno, even if he averages 8 wins a year until he is 90.
As for that elusive overall .600 winning percentage that a coach needs for hall of fame induction, Kirk is barely above .600 right now. All it would take is a 4-8 final season and he would back below .600 again. Of course the hall of fame made an exception for Mike Leach, but Leach was much more entertaining and groundbreaking than Kirk is.
I think somebody had the idea that Kirk should just hang up his head coaching duties and become the assistant OL coach or something like that. Nobody is going to kick Kirk Ferentz out of the building. But in the end, I guess Ferentz has earned the right to go out on his own terms, whatever he decides.