At what point will we have tapped every literary/real-life historical figure monster mashup possible? Never, I suppose, but after Abraham Lincoln, Jane Austen (and her Mr. Darcy), Charlotte Bronte, H.G. Wells, Mark Twain, Lewis Carroll, L. Frank Baum, Mary Shelley, Elvis and now The Beatles have been attacked by vampires, zombies, sea monsters, zombie and aliens, the Frankenstein monster, a mummy, more monsters and more zombies, the trend is officially getting tired.
Still, that hasn't prevented Porter Grand and Lynn Messina from getting into the act with their Louisa May Alcott Little Women riffs, Little Women and Werewolves and Little Vampire Women. As reported by Entertainment Weekly, both Little books are already on shelves so you don't have to wait one more second for the literary carnage and the carnage of literature.
One final thought: If the mashup trend can insert monsters and ghouls into stories where there were none, is there potential with the opposite where nice, mundane things occur in classic horror?
Would anyone read a mashup of H.P. Lovecraft - The sweet phone Call of Cthulhu's mom?
How about Edgar Allan Poe - The Tell-Tale romantic Heart?