My reaction was "Huh? What?"
My default concept of "fandom" is sf convention fandom. If I spread it out a little farther, it includes sf fanzine fandom.
A brief sidetrack into prototype theory: Prototype theory (as I understand it) is that people don't generally use words in terms of definitions--they have best examples of concepts. My "best example" for fandom is a convention. This doesn't mean I think everyone else is obligated to use the word the same way I do, though I'll get confused for a while if they don't.
Since I think of fandom as being about commercial print sf and conventions (I should probably change that to "words" or "verbal" or possibly the media fandom term "literary", though I'm not crazy about the implied status claims of that last) rather than about amateur fiction largely based on commercial fiction, it isn't obvious to me that what Six Apart did is especially a threat to fandom as I understand it except in the general sense that any attempt to shut down communication is a threat. On the other hand, a lot of fanfiction is roaring id stuff, and good taste requirements *are* a threat to it.
I haven't read much fanfiction, but I had the privilege of being in a conversation with Stephanie Burke at Balticon. A lot of what she writes isn't based on other people's stories, but I gather a lot of fanfiction is based on similar uncensored imagination.
Writing this has made me realize something--I like conventions pretty much the way they are, but I bet people who object to costuming and filk are just using a tighter prototype of "interest in print commercial sf" than I do.
Anyway, what's the first thing "fandom" brings to your mind?