Of course, badfic has stayed mostly the same too, which I find quite interesting. With all the different anti-badfic techniques that have cropped up over the years, wouldn't there be some changes? Wouldn't there be fewer Sues? What do you think?
Fanfiction has been around as long as sentient minds have had the ability to make stories. (For more on this, see most of the later issues of Sandman. Or, see also, the Foglio's take on it, from Girl Genius.) I wonder, sometimes, how many stories of the gods and goddesses of ancient cultures - Greek myths, for example - were originals, and how many were story-telling after the fact that got woven in over time.
As for "anti-badfic techniques," I'm honestly not sure what you mean. There's nothing out there stopping people from writing whatever they want, good or bad, and nor should there be. We all go through a learning process as we write. We all start out writing bad stories, and get better as we learn from our mistakes. (Well. Most of us get better. Some of us stop writing, and some of us refuse to learn from our mistakes. See again: the entirety of the history of sentience.)
If you mean stuff like the PPC, that's not really "anti-badfic," not in a sense that would stop people from writing it. (And again - nor should it. The last thing we want to do is silence those we disagree with.) It's just a different kind of fanfic - one that happens to revolve around other folks' fanfic. Meta-meta-meta-fiction. Sort of. But actually stopping badfic? Well, first we'd have to agree on exactly what badfic is, which probably will never happen, since what's good and bad fanfiction is so subjective. (Mostly. The stuff we generally mission, as pointed out several times, is the hilariously-bad, not the mediocre or the "bad but it could be improved." That's for a reason.)
But my point is, most people will never read fringe stories like the PPC, or Sue-slayers. They're written for a very small audience, for the most part, because most people don't actually know fanfiction exists when they start dreaming it up, and may not even know fanfiction exists when they start writing - until they get into a community, and even then, a lot of folks don't much care to distinguish between badfic and goodfic, and the ones that do either leave concrit or flames or just don't bother reading it... and the very few folks who are left over may or may not ever actually care enough to find the PPC. So... we're not really making a huge difference in fandom, in any single fandom. The point, as far as I know, is to entertain each other and vent about stuff we dislike - writing as catharsis. That's never going to stop anyone (and, yet again, nor should it).
As for the thread going on about whether we're allowed to mission these... Please don't.
1) They were written, for the most part, multiple decades ago. The authors who wrote them would probably be deeply embarrassed to know they're still floating around. Lois Bujold got her start in writing there, and IIRC, one of the ones she wrote was the story where Cordelia's Honor started. And although a Klingon and a Vulcan falling in love may be utterly bizarre fanfic, and perhaps something some of us would write scathing reviews of, Cordelia's Honor is an excellent book. It's a cheap shot to go after something so long ago, so far, when we have no idea how the authors feel about it now.
2) Not everything needs our input. To me, it's really awesome that we have records of where the fandom started out! Maybe it's just me being old and crotchety, but I find it a bit irritating that our first thought in finding this interesting history is "How can we best mock it?" Please... don't. Appreciate it, laugh at it... don't go after it. Please.