Even Fifty Shades of Grey already has "fan fic" of its own that I have seen published on Amazon
Here are two so far that are free: (They are not kid-friendly, obviously)
Ten Shades of Sexy
Fifty Shades of Silver Hair and Socks (The author has written other '50 shades' titles as well)
So we have fan fiction, and fan fiction OF fan fiction, and I wouldn't be surprised at fan fiction of fan fiction of fan fiction, etc....