You still need to be a very good writer, of course. But some of the franchises will consider fanfic writers. If you check the previous entry in my LJ, you'll find mention of two people I know who were asked to submit material by pro editors who'd seen their fanfic. In one case it was to an original anthology (and the editor herself was in fanfic before turning pro), in the other it was for the franchise she'd written fanfic in.

And a fair number of the Trek franchise writers from way back did fanfic. The difference was that they also had a pro track record before being asked to write franchise novels.