Position ranks are a horrible and DANGEROUS idea.
I'm supposed to be a diamond/plat/gold player, you name it, but not a platinum MID ONLY player, all this does is make one tricking even more rampant. Not to mention now there's gonna be rng to the queue, will I get my main role and rank that I care about or off role(or god forbid auto fill) and be on a match I don't really care about for 30 minutes? Now what if this happens THREE times in a row, how does that entices me to keep playing ranked when I can't even ATTEMPT to rank up my "main" role? How many people is this gonna push out of ranked? It's not gonna be a fun experience and no matter how many "boosts" you try to give players if they win a match, what if they lose both and now they suddenly lost almost an hour and half of time doing nothing?
That's my main problem with it, the system isn't gonna fix anything and it's gonna make the ranked experience much worse for both the semi casual player and more dedicated people, how many of these games and bad streaks of off pick roles does it takes to make someone quit ranked and maybe even the game?
The answers you gave us on the added parts trying to "clear" some concerns don't actually clear them at all, they give some insight but most of them are "we're planning, we're thinking, we probably will" etc.
There's so much that can go horribly wrong with this change, the one good change is the 2 added tiers but that's about it, no one asked for the role ranks and there's a real risk of completely killing ranked, this not only changes how the queue works but how everyone at all tiers before master is playing, there's gonna be lots of losses because of a secondary rank not caring, lots of wasted time because you get your secondary rank, lots of frustration and possibly even quitting solely because of a change that no one asked and that will fix NONE of the problems it supposedly will "fix", if anything it just accentuates these issues.
Please reconsider these positional ranks, I don't see how this is a good idea or a good result could possibly come out of this, this is possibly way way worse than dynamic queue.