So recently ive heard about everyone going way up in their division, only to lose their promote series thanks to trolls and afkers. I know that trolls don't automatically show up in the promote series, its just chance, but still, I see their concern. What if once you entered a promotion series, you were only matched with players in the same promotion series. That way, everyone's on the same page with putting on their tryhard pants and everything. Might work.

Its not a bad concept.

The only real issue i can see with this is that there are not that many people in their series at any given time. Thus the wait time for a game of promos could get ridiculously long.

Now one solution to that might be to only allow promo series to be played on certain days. Thus stacking up more people to play in those series when they are available. To expand on that, once you earn a promo if you continue playing ranked and its not one of those days then you will not gain or lose lp. Then on the days that promos are opened there is an additional option in the play screen for the promo series(that only allows promo players in of course).

If it was going to happen they would have to have a way to keep short queue times like you have in regular ranked games, or else people would just prefer to play with random ranked players. Or at least I would feel that way.