Norwegian will not up sticks and move to STN or anywhere else, the company are very very pleased with their LGW operation which has exceeded all expectations at this stage and I'm told long haul is selling really well.
It is too early to say that they have made long haul work, but despite all the dreamliner problems and the negative press associated with it, it seems to be doing very well, the 2013 financials are out in a few weeks so we will see.
The question is when does short haul become long haul from a passengers point of view? Norwegian already operate some of the longest 738 sectors in the world (OSL/DBX & TOS/LPA) to name a few, with block times of 7 hours, yes they are limited to around 155-160 seats, but the 737MAX will likely see that increase to full or 8 - 9 hours and if you fly long haul in Y class then whats the difference ?
Loading catering for a full flight and giving the food away/then throwing 20% in the bin is wasteful
If Norwegian prove the concept, then many will follow, there is for now a world of difference between a FR LoCo flight and a NAS one, thats one of the reason they've been successful at LGW amidst the sea of Orange.