First zombies, now extra-terrestrial ritual hunters. Some people really resented their English lessons, didn't they?
But they've got the mythos wrong. It's been well established (Schwarzenegger vs Man in Rubber Suit) that the Predator will only attack armed opponents (rebel guerrilas, Navy Seals, old black cops just trying to clean up their city etc.). Unarmed humans, particularly women, are permanently out of season. Given that a good 70% of the characters in Pride & Prejudice are a) female and b) not accustomed to packing heat, the most likely outcome is that the Predator will merely rip out Darcy's spinal column and sod off back home. Anything else would turn this proposed entertainment into a cynical and crass corruption of a much-loved classic.