For me, I think the spirit of the "7th Player" precludes anyone who's currently considered to be in the core - Chara, Bergeron, Krejci, Rask - from getting it. Expectations should be high for them, and exceeding them should be virtually impossible. The exception I might make would be if one of them had some inspirational comeback story - injured/sick at the start of the season, and then comes back and REALLY takes off.
But, yes, Twitter has diluted the meaning of the 7th player. As long as fifteen year-old girls have thumbs, that's how it's going to be.
I do have to say that I agree with Pastrnak this year. When he was drafted, my expectations were: Goes back to Sweden, becomes Carl Jr., and comes back in a year or two. When he started training camp, my expectations were: Plays in the AHL and maybe gets called up for a game or two. When he was injured by Miller, my expectations were: Maybe he stays in the AHL for a year so he can get some experience learning The System (TM, Patent Pending) and so he can get some weight on him. When he was called up, my expectations were: 9 games and bye-bye, but hope for an explosion next year.
I think each moment, he exceeded my expectations. To me, it doesn't HAVE to be a rookie in his first or second NHL year - Kelly, Campbell, Paille, even Marchand are players to consider. But Pastrnak's floor was set so low, and ceiling has risen so high, that I'd have to give it to him. He's the only Bruin to get a Pasta Trick (4 goals in 2 consecutive games) this year. And he's looking like he WILL be a core player in the future - or at least like he has a damn good shot at it.