increase in seats. Even if those two things you listed happen, the corners will never be "filled in." It would probably be more cost-effective to build an entirely new stadium. What's more likely to happen is a reduction in capacity to add more room for more expensive seats, and possibly more suite/box type areas, whether that's modifying the existing box on the west stands or doing something similar on the east side.

As far as BYU being crazy to do anything to the stadium until it's a P5 program with constant sellouts and waiting lists for season tickets... I have to disagree there too. There's no reason BYU can't make some infrastructure type upgrades to the current structure. Locker room, dining facilities, restrooms, interactive fan displays, team shop, et cetera -- those are areas that would improve the experience for both fans and players that wouldn't require the kind of investment that massive expansion would entail.