In addition to "bad" fanfiction (that of the "any two guys" variety), I admit that I was thinking of a particular uberHercules slash novella. It's far more of an erotic Georgette Heyer parody than anything else-- and, in fact, if you changed the names, you'd never know it was based on Hercules.

The Uber genre seems (to me) to tap into the fandom solely for a ready-made audience, though it could potentially be cleanly copyrighted and sold as original fiction. Of course, that's of limited utility: I'm not certain how broad an appeal these stories have, and that may make professional publication unrealistic.