While NekoMataMata's solution would likely reduce queue times at least in the short term, I don't think they would be reduced enough to outweigh the cons of the solution.

1. A group of 4 friends who are playing in the appropriate role split of 1 tank, 1 healer, and 2 DPS aren't going to split up to do the roulettes. They'll find something else to do together.

2. A group of 3 friends would have to have one of them sit out or do a separate queue themselves. This splits up groups of friends and would likely push those friends to do something else that they can do together instead of the roulette.

So while in the short term it may reduce queues, it may in the long term increase queues as friendships develop and more people drop out of doing roulettes as often so that they can play with their group of friends.