BYU doesn't build anything without having the money upfront. If they got a couple of big donors on board then it could happen, but as said by others, it wouldn't be likely for a couple of years down the road.
On the other hand I would love to see them renovate LES and get rid of all the benches and put in seats around the whole stadium. I really hate fighting for my seat when you get a family large of stature next to you.