Why would any of the BIG10 schools want that? How does getting the conference to 20 teams make it better? I understand getting another time zone and a school like USC. But adding teams that in good years might be at the top of the conference, increase your travel budget 10 to 15 percent, steal some of your best recruits (because they'll start recruiting the Midwest as well), and DON'T add value doesn't make sense.
It's not like the people 20 years from now who will be running sports broadcasters and will be deciding on broadcast contract offers will think, "If only Michigan, Ohio State, Penn State, and Wisconsin had added Oregon and Washington we would have still given them a good contract." As long as there are Americans watching sports the BIG10 is going to be doing better than everyone else financially except, possibly, the SEC.