TLDR; We are changing Position Select to Position Preference, so you can tell us both your strengths and weakness. We will do our best to place you into one of your strengths and you will sometimes play your third or fourth best position. You will never have to play your weakest position.
A year ago we created a new lobby for draft game modes that allows you to pick the primary and secondary positions you want to play. We have since shared some of the positive results and talked about the challenges of striking a balance between getting players into games quickly, creating high quality matches, and giving players choice over which position they want to play. Over the course of the season we have continued to iterate on the system, improving matchmaking times and increasing the likelihood that a player gets their primary position.
We are still faced with a fundamental problem: Not all positions are equally desired at all times. This has caused players wishing to play the highest demand positions to have to wait unacceptably long times to get into games.
To demonstrate the size of this problem: we saw cases where players had to wait in queue nearly as long as they spent playing the game. We are really close to having the right spread of position coverage to keep queue times and match quality in a healthy place.
To help reach this goal, we are bringing Position Preference to normal draft PBE, and you will have an opportunity to play around with it and provide feedback on how it works. The key difference between the old Position Select and the new Position Preference is that players will occasionally play their third or fourth strongest position (maybe one out of twenty times). How this works is you continue to select a primary and secondary position strength preference and you will get these positions most often. You also now have a third option to set one position you do not wish to play, even when you prefer to fill. You will never have to play your weakest position!
This is a compromise we believe will be an overall improvement over the old draft mode, where you were expected to know many positions and there was a chaotic free-for-all to get the position you wanted. This will allow us to make high quality matches faster.
This test is coming ahead of preseason because it is a big change and we want plenty of time to gather feedback. Rest assured, we will not be enabling this feature on live in ranked before the end of the season. We really want to hear your feedback on this and we encourage you to check it out in the pre-game draft lobby on PBE.
I will hang out in the thread for a while if you have questions, and we will be back with more information about other changes as we get closer to preseason.
Básicamente añaden lo que se lleva pidiendo hace mucho tiempo: Poder elegirtu mejor posición-> fill y EXCLUIR un rol, dándote preferencia a tu MEJOR ROL y teniendo la posibilidad de jugar otros 3 roles pero sin poder jugar tu "peor" rol.
Personalmente me parece genial, era de esos players que le molaba jugar de poco un todo a veces, pero poner fill era como asegurarte el support.
Aparte, parece que ese "ban" a un rol que se va a poder hacer TAMBIEN afectará al sistema de autofill (que si no eres plat 1+ nunca lo habrás experimentado seguramente, diría que hasta diamante 3 o así es casi imposible que te toque autofill (en plat 1 a mi me tocó una vez y encima de mid 
)) con lo cual directamente NUNCA jugarás tu posición más odiada/más débil.
A la vista está que Riot ha decidido por fin hacer las cosas bien y escuchar a la comunidad, desde hace unos meses solo toman decisiones buenas.
