Theoretically, you could make the argument that it would've nice if many more members of the Master's Eight were well-known expert trainers in the show rather than just the game champions who received much less characterization in the show. It would've been a nice way to bring back familiar faces from the past series that would give some of the battles more of an emotional hook and/or sense of familiarity to the audience. For example:
Ash
Iris
Tobias
Leon
Cynthia
Kukui
Brandon
Diantha
Who would've been in your ideal Master's Eight lineup?
Ash
Iris
Tobias
Leon
Cynthia
Kukui
Brandon
Diantha
Who would've been in your ideal Master's Eight lineup?