Honestly, what I would like to see is either:

1. In Casual and Ranked you can queue however you want between 1-5 players. Teams can be made however the matchmaking puts them together. Just restrict it so that parties will never go against a team of 5 solo players.

Or

2. Split it between Solo, Duos/Trios or Team (full 5) queues. Each option would have a different ladder for Ranked. They can restrict the rewards to your highest rank between the options for all I care, I just want to queue with friends. Some of my friends won't even touch pvp unless they can group and I imagine they aren't alone.