Yep. Nebraska would be a trap for Campbell. Many of the same geographic/recruiting limitations as Iowa State with far higher expectations. At least at Iowa State he can really compete for conference titles now.
Would really only see him leaving for one of the Big Four Midwestern Jobs (Notre Dame/Michigan/Ohio State/Penn State), and given the notable lack of enthusiasm for him when our job opened up last year I'm not sure that ever happens.
The Midwestern Big Four don't appear to be opening soon unless Day and or Harbaugh go to the NFL, and Harbaugh already made a meal of that earlier this year. I don't know what kind of looks Campbell would get from the NFL, if any, but he's probably going to have to make a move soon while he is still in demand and getting Iowa State to bowl games yearly.
Thought he did a great job at Toledo, thought he was nuts for taking the Iowa State job, but he's managed to do well there by their standards. That being said, his best season at Iowa State was 9-3 in 2020, the year the entire planet was slightly off kilter a tad bit. He's 31-23 in the Big 12. At $4M a year, he's not going to come cheap for the next job he takes if he's in demand.
Transitive process suggests that if he went to a bigger program with a better brand and better resources, he should be able to succeed. He's done that once already. I think he is the kind of coach whose way is going to work at places like Toledo and Iowa State, whereas a bigger program would want to take the chance on Fickell or Fleck or even get Rhule coming out of the NFL.