Off meta is bannable if it means enough people in enough games report you for playing the way you do.
So if you play Soraka this way enough times and get enough reports, you are liable to be banned after a manual review, because Riot found that overwhelmingly the negative reports stacked up against your favor. Especially if there was enough complaining done by your teammates in the pre-game lobby and you still played Soraka (in this manner) against their wishes.
What Riot has stated is that creating a "negative environment" for other players is bannable; but that could mean anything you do over a period of time that comes into direct opposition to anyone you play with, should you get enough reports stacked against you.
Do you play Soraka top/mid? Get enough grievances piled up (reports) about playing this way, you can be punished.
Do you play Yasuo jungle with weird items,etc, and don't do well consistently? You might be punished for feeding/trolling, if you get enough reports stacked against you.
Do you never buy a sightstone on support? You might be punished, again.
It all depends if the particular Riot staff member reviewing your account (if you get enough reports stacked against you), deems that you've been "negative enough" in your style of gameplay or champion picks -- and have determined you've created a "negative environment" or "lack enough communication and teamwork" with your team (by refusing to listen to them and continuing to play what you want and not what they want).
