There are no limits. As long as it's not original fiction or published (so, authorised) work, then you can PPC the badfic. It's sometimes quiite... er... 'fun' to be the only agent working for a particular fandom.

There's no official list of fandoms the PPC covers. The PPC covers anything that needs covering/that they have agents to work in.

The only pseudo-official fandoms are the ones that are so hugely popular that divisions have been created for them in the various departments, like LotR and HP, because they generate so much badfic. Most fandoms don't fall into this category, but that's not because they don't have badfic. It's just not so overwhelmingly common. {= P

Inversely, there are a few fandoms (Twilight, Eragon) that are hugely popular but that no agent will go near, simply because they can't distinguish between the badfic and the canon and can't be trusted not to kill canon characters. That's not to say that the PPC wouldn't cover them if they had people willing to do it, though.

Some fandoms, like Farscape, are lucky enough to have virtually no badfic. Some mediocrefic, but no badfic. I've looked, and I've never once seen any hint of a serious attempt to break up the canon romances, for example. Most of the fic on the Pit is filling-in-the-blanks or AU, with a few "canon adventures" for spice. It's astonishing. That said, if anyone ever does see Farscape badfic, please tell me. I will PPC it with vengeance.

So... yeah. It doesn't matter what fandom the badfic is in. If someone wants to PPC it, that's awesome.

~Neshomeh