I saw the movie twice over the weekend and I made a Scooby-Doo "Ahuhp?" each time I heard 'the aft nacelle'. Cumberbatch imbued (?) Khan with excellent enunciation in this film... if he did not say 'aft nacelle', I need to see (or hear) some good evidence to convince me that he said something else.
And I have no idea what an aft nacelle would be. If it is a goof, it seems like an odd goof to have made its way to the screen, considering how us Trektechies would jump on it!
has well pointed out, however, nacelle could also be some engine housing other than the warp nacelles. I don't think we have ever heard or read a reference to an "aft nacelle" before, but maybe it is a brand new term for something on the jjprise...