I'd have to agree with CentreFix25, over the last few years NCL has seen tremendous growth especially from Lo-co's such as easyJet and Jet2.
Over the next few years I would expect some new routes, but I also expect growth to decrease slightly.
Possible new routes would be:
EWR - Continental 757
WAW - One of the Eastern European Lo-co's
And perhaps charter flights to Croatia, and Hurghada in Egypt.