This would lead to a couple of positive changes for the game:

1. Players will try harder to win their ranked all roles matches.
2. Players will grief less when playing their ranked all roles matches.
3. There will be less matches where you need to play support or hard support since there will be more people queuing for all roles matches.
4. Players will try harder even in their role queue matches since they will appreciate having them even more.

The state of ranked right now is really bad with most games depending on whether your supports actually want to play the game or are there just to pick up the 2 role queue games. Therefore, I think this change is completely necessary.