Quick Response.

It doesn't take long for fans to start producing fanfiction. Joss Whedon's new series Dollhouse has only aired 3 episodes, yet there is already a section at Fanfiction.net for the series with 25 entries. And not surprisingly there is already crossover fic for it, such as this example I spotted at the Buffy: the Vampire Slayer crossover site Twisting the Hellmouth. After all the lead on Dollhouse is Eliza Dushku, who played Faith on Buffy. No doubt if Sarah Michelle Gellar ever goes back to TV whatever she stars in will be quickly crossed over as well. Personally I'd be leery about writing fanfiction this early for a TV series. There's a strong chance whatever you write will be contradicted in short order by subsequent episodes.