You might have heard of the "coffin corner" the U-2 pilots flew in. The U-2, at 90,000 feet, had only 9 knots between stall speed and Vmo. Airliners fly in a similar, but wider corner, with circa 15-30 knots between stall and Vmo. Vmo is where shockwaves start appearing on the upper wing surface, buffeting, engine surge and all kinds of bad stuff happen. Stall speed is relevantly high as low air density means the wing already operates at a high lift coefficient, also the wing has a lower CLmax value in transonic conditions.
The reason for this may not always be purely aerodynamic/stall related, aeroelastic behavior of the wing with high CL and transonic speeds is very complicated (even more so with complex wingtip devices) and I believe this will be the limiting factor.
For specifically designed wings, the wing can achieve higher transonic CL compared to subsonic, but I hugely doubt that an airliner wing is designed like that. Wings designed for high transonic lift are generally seen on fighter planes. As they have a lower aspect ratios and don't have wingtip devices, they are simpler from structural and aeroelastic standpoints.
Coming back to your question, the wing does not have much room to be shrunk, even in cruise conditions. Accommodating for the takeoff and especially landing is not as simple as slapping on high-lift devices, as in that case you'll still need to account for the failure of some high-lift devices and still be able to land the airplane.
The F-104 interceptor was designed with a very small wing (we had a F-104 gate guardian in front of our building in college, I was shocked when I first saw it with my own eyes) and resorts to flaps, slats and a boundary layer control system, which is air bled from the compressor to energize the boundary layer and delay the onset of stall. BLC obviously only worked when the engine was running, so with a flameout the approach speeds of the F-104 exceeded 200 knots. This was a contributing factor to the terrible safety record of the Starfighter, some air forces lost over 30% of the airplanes they acquired in accidents.