Blood Bowl become a success? Who would have ever thought to mix fantasy and American football? I would not have, but it works. I might have thought of it actually, but the next thought would have been "everyone will think that is silly. I should not do that."
Some people do think it is silly, I'm sure, but it has launched a board game, books and a videogame. It has rabid followers. It is unapologetic in what it's about and I think it's a great example.
Maybe that thing that no one else would ever dare to launch...maybe that's EXACTLY the thing to go for.