New Split Ranking and Matchmaking System

Recently Riot has been talking about how they want to split people's MMR into 5, based on the position they play on the map. While I certainly think this is an interesting take and I'd like to see how it performs, I'm worried that with it will come a much more inconsistent matchmaking system, and what happens if you autofill into a game? Will there be an autofill rank or will it look for the MMRs of the position the game needs? Just a few unclarities I'd like to be answered if possible. Thanks.