becomes essentially a non-issue.
The only thing it really limits at that point is BYU not being in the South or Midwest regions. But considering Houston will be the South 1 seed and Iowa St. likely ends up in the Midwest and no other Big 12 team has a chance at a 1 seed, it won't come into plat at all.
And for 1st and 2nd round games, they determine those sites AFTER the top 16 teams (1-4 seeds) are placed in the bracket so they would simply make sure they assigned BYU to a Thu/Sat location.
Once you get to 5 seed and later, you have to worry about Sunday play in the opening 2 rounds more (since locations are already set at that point).