Phil Parker (likely should get the chance if he wanted it, but I don't think he wants the bullshit that goes along with it)
Bob Stoops (too old and too much weirdness and rumor and issues when he left Oklahoma)
Mark Stoops (maybe but meh)
Chris Klieman (great option)
Bert Bielema (FAT!!)
Second Tier Mostly Younger
Brian Ferentz (used to be in the top tier, very unlikely now)
Jerry Montgomery (would be a good option)
David Raih (more likely a OC hire)
Seth Wallace, Levar Woods (more likely DC)
I just don't see them making an outside the program hire, so not even going to list anyone other than Klieman who is a pseudo-Iowa guy.
Don't think it matters though, Kirk isn't leaving for 4-5 years.