I think a team builder draft for ranked would be nice, but it is impractical. The higher elo players already have to wait a long time to play as it is. It would be nice for low elo, (such as silver) but I cannot see them being able to implement it.
However, the idea of having a system where you could pick two roles before game that you prefer could make ranked a little better. You then would at least play a role you wanted to play a majority of the time.
For low elo players such as myself it would make ranked more fun I feel. I can understand why Riot would not want to do this and may take the stance that you should have to be able to play all roles and work with your team. I get it and I do not mind filling since I have played the game a long time and can somewhat play each role. It just gets hard when you lose a bunch of games in a row where you get constantly trolled before the game starts and forced to play roles over & over again you may not be confident in.
I guess the ultimate question is what skills is ranked truly trying to measure. If you were allowed to always lock in your two favorite rolls, then ranked would be more heavily weighted on how well you can play those certain roles alongside your team. The current way, is basically measuring your skills at playing the game at any role and working with your teammates no matter how immature,unskilled,etc. they may be.