A simple easy and effective fix for calling roles is to add in a role queue.
More than 5 roles. Different role compositions exist. This won't happen.
There aren't more than 5 roles, each role stem from the 5 basic roles. If you want to TRY and complicate things, you can just go the regular route. But for all those who do care, believe me, they're the majority, a easy setup is a much needed feature. People who want to experiment can still do so in the regular queues, but the meta isn't going anywhere. Believe that.
3: Splits the population of ranked (people who queue'd up for roles can't be put in the same lobby as people who didn't queue up for roles.)
I take that back now...come to think of it. You can simply add a feature to be included in queues that have players who have selected a role. If you really don't care about what role you get, you can join others who do. Obviously, if you troll your way, that's your own fault and getting banned from your own doings is no problem. While it's true the population would still be split, having a feature to be included will lessen the population split incredibly.
You can tell yourself bananas grow on trees all you want, but that doesn't make it true.
The best ideas are those the community aren't able to grasp. For starters, too many people lack simple logic. They say one thing and mean another. Guess the claims on the community are true. I can give a counter answer that will best almost every counter to this feature but it'd be pointless less Riot looks at it. Guess such a feature only belongs to games who have a higher standard community. Have fun living in the bottoms while the few ascend. In other words, this is closed in my books. The world is getting dumber I guess.