TL;DR: Let players select more than two roles, perhaps by altering the Fill option from the start so that you can select preferential order of the available roles.
I play mid and bot lane. I'll play jungle if I'm autofilled and I'm in a good enough mood not to dodge that one-in-twenty or so chance of getting served jungle. Top lane makes me nauseous. If I could somehow queue something like Mid > Support > Marksman > Jungle > Top, that'd be really convenient, especially since I'm sitting in lobby right now and can't decide which role I want to try and get matchmade for. Matchmaking would be a bit smoother, and autofill can have a vastly reduced chance of dishing out a role the player doesn't want. Everyone wins.