I still wouldn't drop Nebraska. And honestly, if the Big Ten did drop someone Nebraska is probably the least likely after Ohio State, Michigan and Penn State.Nebraska is going nowhere. Miami will get stronger under Cristobal. Miami has Florida to recruit great talent, Nebraska has nothing.
There's really no limit to the number of schools that can be added. If anything, like HailtoPitt said, the top 30 or so schools will eventually break away.