At the time i thought about something similar, as having another competitive mode with lower rarities, the game was still very young to accomplish this properly. Maybe it could be done in the near future as we should get more troop’s reworks.
In a similar way, as in having restriction to team building, a competitive mode like PVP, but with some sort of rotation or ban of troops, could just as well work to add extra variation to teams used on attack or defense. It’s an old idea i had: