If thesy can grow the market then that is great. Maybe those who couldn't afford to fly will now be given a chance to holiday and that is great. I'm all for that. But shifting capacity around and getting the same bums on different plane seats to me is neither here nor there.
In terms of other routes mentioned. I think given a few more years once Iceland becomes more mainstream then it could feature on the NCL route map. Even now it still requires a certain sense of adventure to go there but U2 have no problem filling the BRS and EDI flights but both of those will benefit from more inward tourism.
RAK was launched from BRS and instantly successful seemingly. It's even popular with the odd hen party believe it or not. Hot all year round. Cheap. Historic. Apart from a lack of beach it has it all and could make a good city destination. However myself, and a couple of friends won't go to countries we deem high risk. Not sure how typical this mindset is but if it's common then it could hit demand. And all it would take is one high profile incident and it could collapse over night.
I'm surprised DLM hasn't been tried by U2. Go there any day and there's an minimum 8+ Thomson aircraft on the deck. It must be hugely popular with Brits still and Turkey has long been a popular destination for Northeasterners. They need to make up their minds about easyJet Holidays. They need to push it a la Jet2Holidays as it seems very much an afterthought. If they pushed it then it could achieve a lot.