Manchester is going to be short of stands for the next 10 years or so
Not necessarily. MAG's TP planning application was carefully choreographed to get things moving on the airport's redevelopment without stirring up controversy, but it is a big mistake to presume that everything envisaged for the next ten years is included in that application alone. There will be further incremental planning applications along the way. An apron extension ... conceivably outside the airport's current footprint ... has to be a consideration down the line. If anything like that had been incorporated into the TP application, far greater resistance (and possible delay) would likely have arisen. Meanwhile, did you notice the number of greyed-out structures on the 'fly-through' video accompanying the TP? It really does emphasise that the subject matter is the future look of T2, not the whole airport site.
Do you believe that MAG intends to demolish the T1 site to leave some of the most valuable real estate on the complex undeveloped? I certainly don't. But I find it entirely plausible that the planned replacement T1/T3 structure is still in its infancy on the drawing board. The construction team has plenty to be going on with for now in the form of the T2 redevelopment. But ten years is a long time. Incremental planning applications will follow when the time is right. Conditions in the global economy will heavily influence the timescale ... low oil prices and goldilocks feelgood conditions won't last indefinitely. But if the demand is there, MAG will make provision to accommodate it.