Fitts will be the every down DE. Anae will rotate more.
Utah has a tweener DT/DE who will play DT in the 5 man front and situationally slide to DE in some of the 4-3 and 4-2-5 packages. Utah has a few pass rush specialists that will see heavy reps on passing downs.
Overall, I'd expect Anae to play maybe 60-70% of the reps this year. He's put on enough size to handle that. He'll probably replace Fitts as the every down DE in 2018 when he's grown a little more.
Without go-fast-go-hard, Utah will have the luxury of making all these substitutions, so I don't see anybody being forced to play more downs than expected vs BYU.