I spoke to an engineer a good few years ago who reckoned that we would eventually jump straight to hypersonic sub-orbital jets which could do London - Sydney in a few hours and not develop a new generation of supersonic jets owing to sonic boom problems (and the amount of energy required to produce sonic booms).
I would think that this is a few years off (although a certain Mr Branson has an outfit looking to provide sub-orbital flights).
One of the all business airlines that went bust (maxjet, Eos - I forget which) hasd its own dedicated terminal at Luton and combine this with the latest first class sleeper suits and you probably cannot justify supersonic transport except for ultra long hauls such as Los Angeles - Sydney. However you would need to develop a SST that does not require refuelling en route to be worthwhile (unless you refuel in flight - discuss) and that is a long way off. Its probably easier to develop a hypersonic sub-orbital craft - or the guy I was chatting to thought.
It is certainly intersting to compare aircraft in the 40 years prior to the introduction of the 747 in 1969/70 with the 40 years since and the rate of growth has certainly slackened, but remember that Apollo 11's computer had much less computer power than a modern notebook. The early 747s had plastic tubes linked to speakers in armrests - state of the art at the time. Airframe development has slowed down but avionics & IFE, etc, have advanced at a rapid pace.
With all the concern about environmentalism I see effort going into developing new fuels such as algae together with incremental developments in efficiency. And I have to say I am hopeful that technology will provide answers ans we will still be flying in fifty years.
Even so, I would be very interested if ant ppruner has information when we are likely to be travelling in flying wings and what speed we will likely be doing so. (My guess is about Mach 0.84.)