Unless i completely misunderstood what they said, we gonna they gonna have the exact opposite effect fo what they said (being able to do ranked in multiple roles). Especially for players that likes TO CLIMB with multiple roles (fill players, or duo-tri roles players).
If the new system gives you a different ranking system for each role you play, then it just means very simply that you'll be forced to main 1 role at all times, Example here so you can udnerstand:
Example: I am a player who is confident in his ability to reach pretty much the same level of play (let's say PLATINUM 3) using Support, Top, and Jungle, and i like to keep variety when i rank up.
WIth the new system if my highest queue at the moment is support at plat 3, but my queue as Toplaner is Gold 1, my victories as toplaner has no impact whatsoever on my highest ranking (the one i want to use to climb) meaning this totally kills the ability to do ranked games (and climb) with multiple roles.
So... i'm not the only one who ranks up using multiple roles for sure (Azael the caster said multiple times he maisn top but he likes to play ranked as fill), any explanatiosn or clarifications on this matter would be greatly appreciated