Here's the thing. Encouraging new players to jump into ranked is a bad idea, especially since you lowered the level requirement to play ranked as well as making it easier to get to that level. There shouldn't be missions in regards to ranked at all.
When I just barely hit level 30 way back when, I jumped right into ranked, and then I wouldn't admit it, but I caused a lot of problems then because of my inexperience and because I thought I was better than I actually was. I also wasn't educated enough back then, even after grinding so hard to get to 30 (and since there have been over 60 champs released).
So with a more vicious learning curve, and making ranked easier to access by players (lowering exp requirements to level and changing the level required), I think it's a terrible idea to make missions out of ranked queues, because you are going to have inexperienced players jumping into games and ruining other people's games.
The missions before the new season didn't involve ranked queues, but instead focused on flexibility in regards to runes, and that was a good direction to go, do more stuff like that please.