I picked book 8 because I can see people who really love the series wanting it to go on forever.
I can also see a lot of AU's poping up. Oh noes, they killed Snape off! However can I get him and Hermione together, now? I know! I'll write an AU fic where he doesn't die!! *SQUEE*
Anywho... Everyone's thrown out good ideas. All I have to add is that it will survive.
Oh, and I practially live on HP Lexicon when I'm writing. I'm a stickler for getting my cannon facts straight. Or at least, if it's something I'm making up as I go, I want it to sound as authentic and plausible as possible.