Whilst I think it is great that foreign airlines have at last realised that there are people living North of Birmingham, and have added news services to MAN, and other airports, I think the future of expanded pax services really exists in MAN.
Perhaps MAN doesn't count, as you did say everything North of MAN, but I think that if we are going to be realistic, and exclude London, then I'll have to be honest and say that I don't see exponential expansion in terms of International airlines (and hence pax traffic) at airports such as NCL, LPL, LBD and others.
It's brilliant that GO and Easy have started up at some of these airports, but I think this is mostly low-yield short-haul traffic, which doesn't generate pax traffic to the same scale as International airlines would, if they started flying into NCL, EDI.
Basically, I think either the populations of these towns and cities are not large enough to (in the airlines' opinion) warrant flying, lets say, a QF 744 into NCL 3x a week; or that there is not a high enough proportion of the population wishing to pay premium fares.
In London & Manchester, there are extremely high numbers of people wishing to fly Business or First, and the airlines love this.
But I may be wrong!
I think if we are just talking about any increase in pax traffic, I would put my money on EDI.