Fantasyland already has several dark rides, in fact, more than any other land at the DLS. As the witches pointed out, DL only has one major stage show, and that is Fantasyland Theater, which offers a much needed variety to all the other existing entertainment.
And once again, it's not a matter of having either a dark ride or a stage show. THAT was one of the biggest problems of "Management Think" in the 90's, where if DL opened one new attraction, then management insisted on closing another attraction. THAT kind of thinking did not offer DL the chance to grow, or increase ride capacity. As others have pointed out, the old motorboat area is greatly under utilized. And the Big Thunder Ranch could also be extended back further to create a whole new area! With setting more new attractions out by Big Thunder Ranch, you could could have the attraction build outside the DL boundary and the beginning of the queue in the current border (like several other attractions, Indy, Pirate Haunted Mansion, even part of Splash and Small World.