The shape of an airplane is dictated by physics but that’s a bit like saying chemistry is dictated by physics,or biology is dictated by physics. Currently wing length is dictated by runway widths, cabin lengths by airport bays. The bulk of the cabin is a tube of constant width as this is the cheapest way to make a pressure vessel and you can increase seating capacity by stuffing in another plug. It is unlikely that large passenger aircraft will be allowed with less than two engines and two engines are cheaper to maintain than three or four. The decrease in engines, from four, to three, to two is a result of (1) more reliable engines (2) changes in legislation. Engine diameters have been increasing to push more air through for less fuel. The actual engine thrust is dictated, for a two engine craft, by the requirement to continue climbing at a reasonable rate, fully loaded, with the loss of one engine. There have been minor gains in aerodynamics and major gains in fuel efficiency but the L/D ( lift to drag) ratio for airliners is stuck at around 20. This contrasts with gliders which have L/D’s of 60 and above. Current aircraft shapes are neither aerodynamically efficient or volumetrically efficient, hence the potential of designs like Boeings BWB ( Blended Wing Body). As to a possible supersonic aircraft, say Mach 1.6, the gain in range due to speed is more or less exactly balanced by the loss in L/D, down from 20 to 10. However there are further penalties in the necessary lower engine bypass ratio and a loss in structural efficiency due to the required slenderness of the aircraft, so the per-passenger weight of the aircraft goes up. We may see supersonic business jets. I would like to see something comfortable. I am a lot happier at 48 hours on a train versus six in a modern passenger jet.
They’re going to look very similar to the ones of today. The shape and design of airliners are dictated by physics, and those rules aren’t going to change.
Aerodynamically the current airliner shape is already pretty well optimized. They’re still eking out slight improvements here and there, there’s much all that much left. Engines probably have a higher ceiling for improvements, but their general shape isn’t going to change much. Reducing weight is a fairly big deal right now, which is where the B787 gets a lot of it’s efficiencies from, and why so much of it is built from carbon fiber.
You can see how similar the original B737 (launched in 1968):
Looks to the brand spanking new B787:
Regarding supersonic airliners, that’s really a pipe dream. Customers showed a while ago that price trumps pretty much all other considerations when it comes to air travel. There simply isn’t enough money to be made developing and flying a supersonic airliners with it’s higher operating costs and much lower number of seats. In addition, supersonic airliners would basically be relegated to only overseas routes due to their sonic boom.