Well, I was just commenting on the hypothetical "If the Big 12 folds" which I don't think will happen in the near future, but the chance is better than 0% as well.
As for the Big 10 expanding, I'm not sure they do that again unless it is a top tier team. The only media markets they might want to move into that aren't Texas are deep in SEC territory and that just isn't going to happen. So, outside of a Big 12 collapse, that as you said, would only happen if Texas and Oklahoma leave I don't think the Big 10 expands again.
Now, numbers like $50 million a year for media rights might start to really look good for Texas and Oklahoma but I doubt anything would change until the next Big 10 media deal is coming up. The Big 10 may look to see if they can improve the value of the conference again before they negotiate the next deal.