I could see it being Pitt. PSU is OK with it if JoePa is to be believed so that is a huge obstacle. They can still play WVU non conference every year.
As far as ISU goes, as a former Iowan, I always thought that ISU to the Big 10 was just silly talk. I don't know if they have veto power but I think the University of Iowa would veto that idea. It's not really a good fit since ISU has more of an emphasis in agricultural, veterinary medicine and engineering. There's no law school there and the only medical degree you can get there is a doctor of veterinary medicine degree. Believe me, they are looking for more things than just athletics when they are trying to get a 12th team. And don't forget, they have been in the Big 12 since it was the Big 6. There's a lot of tradition there.
I still have problems believing that any of the teams mentioned will join. I think the western schools mentioned like TCU and Boise St. are ridiculous suggestions. It's more than just football and basketball. It's tennis and golf and swimming and soccer and volleyball and even wrestling. Penn St. is isolated enough as it is, how do you think they are going to like going out to Boise for a soccer game with budgets being cut the way they have been? Would they go after any of the MAC schools? I'm thinking maybe Miami or Ohio U.