I could see Nebraska moving back to the Big 12, under the right circumstances (and those are actually happening right now).

Big 12=
needs to add a relevant school or so. Doesn't HAVE to be a current Top 10 school, it needs to be someone solid and established. Nebraska is that.
Geographic fit is a plus, especially for other sports. Obviously, Nebraska fits that.
Competitive balance; you don't want to bring in a weakling that does nothing overall for your conference. And although Nebraska floundered in the Big 10 (breaking that condition, in that case), they match up very well against the Big 12 teams, as shown by their records against everyone involved.

Nebraska=
wants respect and prominence. They left originally since they were pissed about Texas, but they walked into a situation where they may have got more money, but lost influence. They're now an afterthought, not a featured member. They probably could upgrade their standing if they returned to the Big 12.

Money- everyone talks about this, like it's in a vacuum. Big 10 makes more than Big 12.
Great, but if the Big 10 sits this season out and the Big 12 plays, and the world doesn't collapse, then TV money probably gets re-negotiated, and we could see some shifts.