If we're talking about fantasy airport extensions, it might be good to have at least one decent international airport in Yorkshire rather than expanding MAN and/or BHX. Failing that, you would need to significantly improve the transport infrastructure around those airports to make other parts of the North easier to reach. Fast, reliable (!) train services for example. Car hire services suited to business people not just holidaymakers, i.e. reception desks in the same building as the terminal and cars you can drive away from just outside - not waiting an hour for a half an hour bus to where the car hire places are in a different village.