Are you folks dead set on including pixiv stats in the rarity metric? It seems odd and not quite fair to me that Japanese fanart production levels (sure, pixiv has some number of non-Japanese users but I hope we can all agree that in terms of active userbase, it's situated in a Japanese-language fannish sphere) should determine whether a fandom counts as rare in an English-speaking fandom context. Especially if the pixiv number is the only number that would disqualify an otherwise eligible fandom. I mean, I get what you say about a certain amount of English-speaking-fandom fannish engagement (or rather, fanwork consumption) happening by way of pixiv, but consumption's not the same as production--and isn't this challenge in part about promoting production? i.e. English-speaking fans may be viewing/circulating Japanese fanart, but if the English-speaking fans aren't actually producing fanwork at levels that would disqualify the fandom....
I guess it doesn't seem right to me that pixiv is the only instance in which a fandom's popularity in the source country/language can, in effect, negate the fandom's rarity elsewhere. With visual content it's easier for fanwork to move across language lines, sure, and I get why you'd want to take that fact into account...but pixiv is a Japanese fansite, even if it's also being accessed by English-speaking fans, and what the numbers of fanwork on pixiv reflect is popularity in Japanese-speaking fandom. I mean, if you're going to use pixiv fanart numbers to determine rarity, why not also use Nico Nico Douga numbers for vids? It's as accessible to international fans as pixiv is, i.e. you need a login to view, but you need a login on pixiv to view full-size art...I think Nico Nico now has an English-language beta interface, too. (No, I'm not volunteering to run threshold searches on Nico Nico!)
Anyway, if you are dead set on including stats from any of these sites--i.e. stats that basically reflect popularity in Japanese-language fannish spheres--better set the threshold waaaay high. 5000 on pixiv would be too low: Natsume Yuujinchou for instance is going to hit 5000 in a matter of weeks, and how is Natsume Yuujinchou not a rare fandom (in English-speaking fannish spheres)? 85 fics on ff.net, 4725 artworks on pixiv.
Most extreme discrepancy award goes to Puella Magi Madoka Magica: 146 fics on ff.net, 67,994 artworks on pixiv aaaahaha.
TL;DR I realize this challenge is not only about J-stuff! and you all have a lot on your plate and it's great that you're running this challenge and whatever you decide will be great.
You said you were hoping for more perspectives, so XD
I guess it doesn't seem right to me that pixiv is the only instance in which a fandom's popularity in the source country/language can, in effect, negate the fandom's rarity elsewhere. With visual content it's easier for fanwork to move across language lines, sure, and I get why you'd want to take that fact into account...but pixiv is a Japanese fansite, even if it's also being accessed by English-speaking fans, and what the numbers of fanwork on pixiv reflect is popularity in Japanese-speaking fandom. I mean, if you're going to use pixiv fanart numbers to determine rarity, why not also use Nico Nico Douga numbers for vids? It's as accessible to international fans as pixiv is, i.e. you need a login to view, but you need a login on pixiv to view full-size art...I think Nico Nico now has an English-language beta interface, too. (No, I'm not volunteering to run threshold searches on Nico Nico!)
Anyway, if you are dead set on including stats from any of these sites--i.e. stats that basically reflect popularity in Japanese-language fannish spheres--better set the threshold waaaay high. 5000 on pixiv would be too low: Natsume Yuujinchou for instance is going to hit 5000 in a matter of weeks, and how is Natsume Yuujinchou not a rare fandom (in English-speaking fannish spheres)? 85 fics on ff.net, 4725 artworks on pixiv.
Most extreme discrepancy award goes to Puella Magi Madoka Magica: 146 fics on ff.net, 67,994 artworks on pixiv aaaahaha.
TL;DR I realize this challenge is not only about J-stuff! and you all have a lot on your plate and it's great that you're running this challenge and whatever you decide will be great.