E.D. Kain thinks it has a shelf-life:
There's a reason fantasy wasn't mainstream before. It's a genre that appeals to people who play D&D and get their kicks reading about elves with names like Tanis Half-Elven and Galadriel. Unless publishers can keep finding the next big crossover, fantasy may once again return to its less mainstream, and considerably less profitable, roots. People can only take in so many teenage vampire romances and wizarding schools. It's possible that the next Harry Potter is just around the corner, of course, but it seems like no matter how many "Is Such-and-Such the Next Harry Potter?" articles I read, the books never quite gain enough momentum to go mainstream. Books like Lev Grossman's The Magicians gain wide critical acclaim, but then run into the immovable object that is the hardcore fantasy fan base.
The Dish 