Let's be honest here. The P5 Ship has sailed for BYU, there is no conference that is currently P5 status that will be coming knocking on BYU's door in the future. I hope I am wrong and will gladly eat crow if it happens, but it won't.
BYU is either better off staying where they are at INDY and being happy with things presently constituted, or they need to jump to a conference, and the MWC would be the worst choice IMO between the two left viable conferences.