What many people don’t realize is LES sits on pretty unstable soil. Utah valley is full of mountain sediment deposited by runoff. Essentially it is a lose gravel pit. The reason why LES has aluminum stadium rows rather than concrete ones was not only because it was cheaper; it weighed much less and could be supported by the soil. To facilitate major renovation that would add significant weight to the stadium, ground soil stabilization via stone columns and piles in the ground would be required. You would have to tear down the who stadium.
Rather than do that, I think the LONG LONG LONG term plan should be to build a new stadium and field house on the ground Provo High sits (BYU already owns it). Replace the SFH with a state-of-the-art student athletic building. These new structures could have the soil prepared properly and be close to each other. There is the space, see below: