The change in the Earth's magnetic field is already starting, with some parts reverse-polarised and a complete flip from pole to pole expected within the next couple of hundred years. Thankfully, GPS and IRS means we'll still be able to navigate advanced aircraft, but magnetic compasses will for some time be useless. Looming sooner are fuel issues, outbreak of large scale war in the Middle East and North Africa, and a return to the Cold War.
On a technological front, high fuel efficiency could see narrow-bodies doing point to point long haul work, and noise reduction will see the end to complete airport curfews.