I think they would invite Montana first, then us and then perhaps the extension. CP would have to expand both basketball and football facilities with no stadium or arena nearby to rent out or use in its place. They'd have to make some pretty lofty promises to join the WAC. Montana is ready for such a move now, dung pile only needs 5,000 more seats in its purposely expandable stadium and we have memorial or Arco nearby ready to be rented. All our other facilities would meet the requirements to join. (Erector set or not, its big enough even if its not pretty)
In the Sky, Eastern, Montana State, Portland State and Weber State are all also in a position to be invited to the WAC. Eastern would only need to add a few thousand seats to their football stadium, and Portland would be in our predicament, new arena or rent out the local arena. Montana State and Weber would both be ready to go with their current facilities even if they are a little on the small side. NAU technically has facilities that are big enough, but they would be another Idaho. I don't think the WAC wants another Idaho.
Personally, I'm starting to develop the opinion that we stay put in the Sky for the time being. Lets become a big fish in a small pond before we become a smaller minnow in a greater ocean.