They've already told us here. I'll quote the important part for you:
We’ve been working on some improvements to competitive system that we want to roll out for the 2016 season. Front and center to these changes, however, is getting all of ranked play onto the teambuilder mode. You’ll be able to pick 2 positions - including ‘fill’ - to ensure you’re playing in the position you can contribute the most in. ‘Feed’ will probably not be an option, (sorry!).
So the answer to your question is next season!
And based on the brief description, it sounds like you'll queue for a role (or two roles), rather than a specific champion. Presumably, once you have a team with players assigned to the individual roles, you'll still have a pick/ban phase just like today. Of course, more details will probably surface as the next season nears.