An interesting idea. This was partially one of the original ideas behind the war rewards - to let players choose what they need the most as a way to make it a very desirable game mode.
For those asking, the update that includes these changes should come around the first week of February if everything goes as scheduled / planned.
After getting further into the data, the full changes should look like:
4 difficulties for Mountain and Challenges
Because each boss fight is spread over different different Team Levels, it's a bit different, so we will be adding Invokus 8, Venusia 8, Aurum 8, Invokus 9, Venusia 9, Aurum 9, Invokus 10, and Venusia 10.
These changes follow the same team level unlock pattern that exists on preceding levels.