I agree about fandom being more a state of mind and a way of relating to stories, rather than a single specific-canon-focused community. That's something I've found Dreamwidth is particularly good for, actually—like, on Tumblr I only really follow people in the same fandoms as me because otherwise my dash gets flooded with stuff I don't understand and have no context for, but here I can see people I know talking about the other things they love, and there's more of that sense of community, and I can appreciate that sort of fannishness even if I don't also know those works. (and it's a pretty good way of picking up new fandoms, of course!)