Nobody believes that NK has some militant sleeper cell in the US waiting to kick into gear as soon as the movie starts playing. Sony doesn't want it released because they're worried even more embarrassing "racist" emails will be leaked, while the big theater chains don't want to open themselves up to potential litigation no matter how minor the risk.
Best idea I've heard is for Sony to release it for free all over the internet as a big "F-U" to North Korea, but again they won't do so because they know the hackers have a tons of embarrassing/incriminating info that they haven't yet released.