Yes. I'm currently in that state of having quit now. On the other hand, it depends on if you mean quit everything about Pokemon, or quit everything official about Pokemon. Clearly, I'm talking about the latter, else I wouldn't be here.
Honestly, Game Freak, Creatures Inc, The Pokemon Company, Jr. Kikachu et. al have nothing for me anymore. I don't think I've outgrown the series so much as I think I've stopped caring. There's just no need for me to spend money on stuff that no longer entertains me. Having said that, I'm far from a person who'll bash on the franchise side of things (save for the endless sequels thing, but every series gets that from me, I'm no respector of franchises, here), and I'm genuinely happy that people are still enjoying Pokemon for generations to come. I'm also not really a nostalgic, either, so don't lump me with that crowd.
I haven't, however, and probably won't quit fan perspectives on the series, though. I'm in too deep, too heavily invested at this point. I still like to talk about things beyond the series, such as morality in hypothetical relations between Pokemon and humans, or characterization of the Pokemon themselves. And as far as the creative side of things, oh-ho, I can immerse myself in that all day long and never get tired of it.
I'm really more of an outsider, I guess. Ya'll can have your fun with the games. I'm gonna just hang out over here and paint this Pokemon mural that represents how I feel about Pokemon culture. And then I'm gonna have people critique it while we all sip grape juice and pretend to be intellectual while busting up laughing over how ridiculous we all sound. And yes, some kind of Nido will be in said mural, 'cuz that's how I do things.