Should have been implemented when autofill was first introduced. You can't expect people who are playing a role they weren't expecting, and probably aren't even good at, to perform at the level their rank suggests. They tried to solve this with positional matchmaking, but that totally backfired as people threw games outside their main role because it didn't really affect the rank they cared about.
I'm curious how they plan to solve people swapping in champ select. Say you have one autofilled player on each team who absolutely can't play the roles they were given. One team has someone who is adept at that role and willing to swap. The other team doesn't. Now, one team has a bit of an advantage over the other in the sense of players uncomfortable in their role.
They should really have it set up so that the players rank each role from most to least wanted, and the matchmaker keeps a separate tally of what you usually play, and it balances these values between the two teams (e.g., you'd never get somebody who get autofilled to jungle but normally mains jungle against an autofilled enemy who never plays jungle).