Regarding only holiday traffic, new destinations could (or should) work from Northern Ireland. Rather than huge amounts of seats on sale for Malaga, Alicante, Palma, Faro; why does demand not exist for a full summer Naples, a summer Fuerteventura, Corfu, Paphos etc, even once or twice weekly. Compared to the mainland airports, we seem to have more seats to fewer destinations, rather than a more even spread. Yes the Costa's and Spanish Islands will always be popular, but our we (NI passengers) really that boring and unadventurous with our holiday choices, and now in many cases at least three carriers competing on the same routes.
Jet2 are the only airline that offer niche, more unusual routes from Belfast, Toulouse, Pisa, Dubrovnik etc, and as these are available after a number of years, I would assume they are profit making. It is these routes that I would actively encourage people to support, so at least there is some choice beyond the mass markets.