Speed: Limiting Factors
We've seen many advances in engines, avionics and materials over the past half century.
However, despite the seemingly mega leaps in these areas; particularly engines and control systems, the speed of airliners has not really increased (although there are rare exceptions of course!) past the M 0.8 mark
What would you say were the real constraining factors here?
Obviously, taking an aircraft over M 1 has consequences, but what technical factors are there to stop modern airliners cruising at closer to this?
It just struck me that the next gen of a/c rolling out of Toulouse / BFI don't get one to their destination much faster than 30-40 years ago. (Although there may be considerably less noise / smoke)
Cheers