They have had disagreements with BYU about stadium modifications in the past, and my sense is that anything that affects sunlight (think permanent ice during the winter in the shadow of the stadium on the east side) will be a difficult sell for that neighborhood. This doesn't take into account views of the sky that would be modified and even potential yard problems (grass/trees/shrubs, etc. not growing properly).
Before the stadium expansion in the early 80's, there was a plan to make both the West and East sides double-decker (it reminds me a little of the double-decker look of Husky Stadium). There was also a plan to include end-zone seating (with a dig-down of the existing stadium field level to a lower level — allowing for more seating closer to the field). Obviously, the double-decker plan wasn't implemented. I remember serious concern over the double-decker architectural plan by the very same neighborhood. I also remember the neighborhood complaining about the LED strips (ring) surrounding the standing — too much light — put in just a few years ago. I'm wondering if they complained about the large TV screen now up and showing replays during the game (especially night games).
My point is that any change to the stadium that affects the neighborhood (sunlight, views, etc.) or noise/light, will be met with resistance from them and that will make the project a lot more difficult to complete.
I wonder if there are a group of Ute or Aggie fans in that neighborhood secretly trying to torpedo stadium improvements.