Augh. I really hope
this is not going to make Yuletide way-less-fun-for-me this year.
I am not a media-fandom person. I do Yuletide for the book-fandom fic. When there are TV series or movies that I particularly like, they tend not to be the ones that fandom-as-an-aggregate goes nuts for. I'm pretty sure that the AO3 is not the be-all-and-end-all even of fanfiction archives, let alone a hugely significant repository of all online fanfiction. I don't think that the proportions of fic in given fandoms on the AO3 is representative of much at all. Maybe in a few years. Not now, not yet.
The one-year rule for Yuletide is bad enough -- the Latest Shiny Thing can get tons of attention because it isn't older than a year, even though it's getting tons of attention elsewhere as well. The Latest Shiny Thing is almost never anything that appeals to me. (Indeed, I tend to react in a contrary manner and decide the Latest Shiny Thing has got to be hugely overrated. Since Sturgeon's Law is always already on my side -- or anyone's, in deciding a given work of fiction in any medium is going to be overrated -- it's rare that I'm pleasantly surprised to find myself mistaken.) If the Latest Shiny Things I can think of were things I had liked, I would probably be happy about the one-year rule, and about the new AO3-as-fandom-size-criteria development.
I have done Yuletide for three years now and it's been a highlight of my holidays. I start looking forward to it ... right about now, Septemberish. I want to be able to look forward to it again this year. Meh.