The real problem is comfort. Planes are incredibly uncomfortable, even if you pay thousands of upgraded seating. I'd rather flights take 2-4x as long but be 10-20x more comfortable.
I'd like to see true innovation, using high-speed blimps or massive ocean-going ground effect airplanes, hovercraft, or something.
I'd rather take 1 day "air cruise" to Europe than a 4 hour hair-raising rollercoaster ride.