The mission which required 25 assists made me queue up for support

Which is when I thought, why don't they make more missions like this so more people are willing to go support?

The objective could be something like; get x vision score, get x assists, apply x seconds of cc, or even make it as simple and direct as "win 5 games as support" The reward? Chests and key fragments. I've read a post earlier about how someone got a chest with every support in the game, but they don't play other roles so they can't get anymore chests without buying them.

Make missions designed to make people queue for support, reward them with chests and key fragments, and this benefits the majority of the player base.

For the people that queue up for support, they will be rewarded with chests and key fragments simply by playing the game. For the people that don't want to queue for support, they won't have to worry about autofill as much, so they can play what they want.

This would also help reduce the amount of trolls in champion select, since there would be less autofill and more people would get the roles they want.

The missions will be optional, so I can't think of any reason not to add them