I don't think the situation with SF is as concrete as you present it. We have no hard evidence (that I'm aware of) suggesting this would be his dream job or that he is even interested in taking the position here.
The position would also come with an extreme amount of unique pressure. He could end up having the opportunity to go to almost any university if his stock keeps trending upward but, if he chose Nebraska, he would have lofty expectations placed on his shoulders from the beginning. Failure would tarnish a relatively positive legacy. No other university would have that same kind of anxiety attached to it. Maybe he doesn't care or maybe he does. Either way, I don't think that's an easy decision for him to make.
Regardless of it all, I don't think there's any chance Frost comes to Nebraska so long as SE is running the show. MR is his guy and I think a large portion of SE's job security is tied into MR's success. If both of them left, I think you'd also have to bank on the incoming AD being open and cognizant of Frost as a candidate. That might be easier said than done.
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