I think this would be a cool idea. It'd be a good way for people who only play x amount of characters, like me, to not feel like leaving because they can't play what they want to. This might sound selfish, but some people just like playing this or that character a majority of the time because they have fun with that character, and not with others. This is the only game I know that punishes you for dodging, AKA leaving in the pre-match setup, because you can't play the character(s) you want.
This can be solved with a quickplay, pick your role and character before the match, total disregard for the fact you can be in a good or bad matchup in your lane, for the people who just like to play this or that character because they have fun with that one.
Thoughts? I know it's unlikely especially with autochest on the way, but I think it'd be cool. It'd be particularly good for people who just want to try a new character but are unable because the character is picked before they can take it or it's banned or whatever.