If Norwegian's facebook page is to be believed this reply to a post suggests the new long haul routes due to be announced are transatlantic and also that we should find out what they are very soon. I'd say one is most likely LGW-OAK unless it is an entirely new destination in which case BOS/LAS/ORD would be a possibility (all speculation of course).
http://gyazo.com/2530b6ae1e8711783cb00ed9c6ca90e0