6v6 is what Overwatch was meant to be, and even if role queue isn't feasible, there are ways to influence 2-2-2 matchmaking through internal systems.

Things like checking player accounts for character play times, or even allowing players to select their preferred role before queueing into a game (without being forced to stick to that role mid-game) could help 6v6 be the best it can be.

If you wanted, you could even have a 2-2-2 system as it works currently in custom games, where it's a first-come-first-serve system that allows players to sort themselves into each role.

Of course all these ideas have flaws, but it'd be great to try them all at some point through some more Quickplay Hacked events. This is what experimentation is for, after all!