The sonic cruiser was nothing but a smoke screen. I don't think Boeing ever looked at it in any real sense. The speed differential was never enough to convince anyone to move from current designs.
CFD is a great tool, but it is in no way perfect yet. Why do manufacturers still spend enormous amounts of time in the wind tunnels and water tunnels? I believe that for the 777 they spent 10x as long in the wind tunnel than they did with the 747.
Seat costs have dropped by a factor of 3 since the inception of the 707, a pretty big advance, but as stated before that is mainly due to the engines and not the airframes themselves. Sure they are a bit better, but the materials used are fundamentally the same and apart from tweaking so are the aerodynamics.
A blended wing body has some pretty serious technical issues to overcome, but I can't see that is totally unfeasible. The same with Slew wing machines, yes the research may have been done in 1982 but the principle is sound. For example the fuel cell was designed in the 50's, but that is seen as the 'latest solution' to overcome piston engines in cars.