What's to stop the airport holding company from gradually buying up and then renting out all the homes in the few residential streets (Wells Ave, Eastwoodbury Lane, etc) to the immediate south of the apron as well as the retail units next to the terminal, over the next 10-20 years as they gradually come up for sale and then, maybe in 2030, demolishing the houses + retail units and expanding the airport's footprint ?
Impose a hefty drop-off fee to discourage cars and claim to be a green airport because 80% of pax travel to/from the airport by train
Ok - I'm being a bit flippant here, but you get the idea... 10m pax in 2040 is not impossible