People say that Tumblr limits discussion, but I do see that kind of thing there. Not a ton, because I don't follow talky people on it and you have to look for it/stimulate it, but you can find it. OUAT gets quite a lot.

Which is I think more to the point - HP encouraged a ton of spec and theorizing and universe-meta, but most canons just don't. Doctor Who does, but imo the intense ALL ABOUT -ISM the more social media-meta side of the fandom has going on is off-putting to people who want to delve into character arcs and motivations (since "no, you're wrong, it just happened because the writer sucks" is always a potential answer).