Have we seen the last significant experiments in the configuration of jet airliners? By the 1940s, passenger airliners had pretty much settled down on the shape that has dominated the industry since then: a monoplane, with wing-mounted engines, a roughly cylindrical single fuselage and a tailplane.

The 707 set the template for jet airliners: low wings, and pylon-mounted engines.


Source: Wikipedia

Apart from the few, smaller, models that place their engines on the rear of the fuselage, there are almost no models currently in production that adopt a different template (in fact, the only one I am aware of is the Antonov An-148).

There are no more tri-jets. There are no more radical experiments like Concorde on the horizon, never mind in production. There are no serious proposals for significantly different shapes or configurations.

The only significant configuration choice for medium-to-large size airliners seems to be two engines or four.

Since the 707 slung its engines under the wing on pylons in the 1950s, the only significant development that I can think of is the adoption of winglets in the 1980s.

You might consider the 747's hump and the A380's twin decks to be significant variations, but they are still only variations on the theme, not fundamentally different configurations.

Assuming that jet engines remain viable in 40 years' time, will the airliners of 2058 still look fundamentally like 707s?

If you're concerned that question seems too open to mere speculation, let me ask it another way: is there a fundamental design reason why the low-wing/pylon-mounted engine/cylindrical fuselage/tailplane configuration established by the 707 shows no sign of being displaced by alternatives?

Or, why have the enormous advances in (for example) materials and aerodynamics made so little difference to the fundamental shape of airliners?
With current fuel prices: Yes, we have arrived at a mature design which will not change much. Recent trends like the increase in aspect ratio and engine bypass ratio will continue, but the general arrangement will remain unchanged.

Just look what happened in the first 50 years of airline operations, and how much changed after that in regards of aircraft configurations:





If fuel prices rise to 200 USD per barrel and more, expect slower airliners with less sweep, much higher aspect ratio and probably even braced wings. To enable bracing the wings will be mounted on top of the fuselage, like on the Hurel-Dubois HD.31.



Boeing SUGAR Freeze concept. Note the third engine in the back which ingests the fuselage boundary layer, thereby reducing separation and pressure drag.

While you might read about two more new design directions, a supersonic airliner and the blended wing-body (BWB), I am rather skeptical that any of those will be adopted in the future.