Back when I started in S3, Pick Order was a thing. We all knew there was a chance we could be put into any role, we said our "pref X Y Z" but that meant nothing. Pick Order was God and it decided our fates. So most people who cared about Ranked could comfortably play all roles in case no one was willing to compromise. Good times for me because I mained Support then.
Auto-fill is different because last season we were able to pick our roles and therefore only played those 2 roles (for the most part). So most people learned only a few champions into 2 roles and played them for an entire year. Now with Auto-fill activated not only are you not sure what role you are going to get, but not many people have experience with every role right now. If Auto-fill is here to stay, I'd say around mid season people will start to play all roles again.
Some advice for those who get auto-filled: DODGE! Don't waste your time playing a role you don't want to. You are going to lose the game for your team and cost you and them precious LP. Just dodge and take the 3 LP punishment, it is 100x better than wasting 40+ minutes for a highly potential loss. Some of you may be thinking "Why do I need to dodge because Auto-fill is a stupid system?" well the answer is simple: It is your fault you can't play all the roles comfortably... Take the time to learn every role with at least 2 champions or dodge when you get autofilled, those should be your two options because playing a champion and role you are uncomfortable with is not ok.