We have the ability to change what items show in the shop per champion
We can change our masteries in the lobby
So why not allow us to setup champion lists? We can place a bunch of champions onto the list for "what we want to play" if we get assigned to a particular role.
Then, in the lobby, when selecting our champion we can only see that list of champions (unless you're banned and picked out, where it will go back to the main list)
This way I can have a list of all the champions im trying to play for that particular role on a smaller list, so i dont need to scroll through ADCs and junglers when im playing support to decide what i want to play.