"Auto Fill" in ranked is just a bad idea, and can create potentially toxic games.
Its seems incredibly counter-intuitive to make a system auto-fill you just to drop Queue times, in the queue where people play their 2 BEST positions to climb to prove your skill.
People play ranked for many different reasons, but to be auto filled and put into a position that you possible haven't played for seasons. That's ridiculous.
Because as soon as someone is 0-4 or whatever, people tilt, say GG at 10 mins or worse. Why? Because every death, objective, or even CS advantages push a team closer or further from victory.
So you want to have a system to reduce queue times but might make people play an odd position which can result in toxic games? All my games this season so far have been really toxic and a couple had people playing out of their comfort zones in roles they don't usually touch.
Something to think about.