i really dont think this is a bad idea if done right for normal games. if done right... there would have to be 2 types of queues. 1 where people get to choose before hand, and another where u dont choose before hand... and those 2 groups would never get into the same game. secondly it couldn't work like WoW dungeon finder in regards to choosing more than 1 role at a time, because there could be real complications being that the computer doesn't select what role ur playing for you by itself, so you should only be able to choose 1 role.... unless it writes (SUPPORT) next to your name once you enter the champion select screen. Finally, there would need to be a pretext that support means u are going to not CS (much), build support items, and buy wards. If this is not done after choosing support, it should be a bannable offense, or else people would abuse/troll or and choose support for short queue times (even though they could get a short queue time by not choosing any role and going into the other queue). But people would have to keep an open mind as to what being a support means, or the meta will never change.
PS: to say no one likes to play support, its not true. when i have a game with a bad support in it that doesnt know how to wards and we lose the game because of it, i generally feel like playing support so dont discount an idea by saying "no one likes to play support anyhow so why would they put this feature in"