Well NAS still have a few 300's so JSY or BHD wouldn't be a problem, but they are due to be phased out, having said that they were due to be gone by now!
NAS have a preference for using air bridges so i think EMA is unlikely, if its not MAN then I think BHX is most likely, unless Jet2 get there before them? NAS have the aircraft with 6 or 7 new 738 due before Xmas and around 8 units due in 2014, long term i think BHX makes far more sense than EMA, Monarch,Jet2 & FR already provide huge lift to the MED. Monarch at BHX would be an easier target and Monarch customer base is much closer to Norwegian's than say FR.
BHX-ARN would be very easy for them, ditto GOT,OSL,HEL
NAS cost per seat is now below that of Easyjet (just) and have gone into LGW and added 176,000 pax in Q2 yoy, can't see it before S14 but they could run some Canary flights to test the water this winter?