DynamicQ. Why can't you make the system do this?
5v5 100% of the time
Games of 2s and 3s v 2s and 3s 100% of the time
Solo players play solo players 100% of the time.
Now solo players aren't forced to play with 3s and 4s premade.
(this doesn't address the fact that MMR ratings are completely irrelevant in the new system. Just a way to make playing as a solo more enjoyable)