But it the changes made to the 747-300 were used in the 747-400 so they benefitted the 747 program as a whole. The 747-300 got enough orders so Boeing didn't have to shut down and restart the 747 line once the 747-400 was ready.
The 757-300 was the end of the line for 757 models. Boeing tried to market a 757-200ER based on the strengthed wings and increased maximum takeoff weight of the 757-300, but no one was interested.
The 767-400 did have an updated 777 style glass cockpit, but that hasn't been offered on any other 767 model except the proposed KC-767 offered to the USAF as a tanker to replace the KC-135E. Supposedly the 767-400 will be the airframe for the E-10 which is a replacement for both the E-3 AWACS and E-8 Joint STARS. Considering the low utilization rates of miliatry planes compared to civilian planes, they should be flying for at least 50 years. Boeing should consider putting the GENx engine derivative developed for the 747-8 on both the KC-767 and E-10 proposals.
I really wish the 747SP had more orders.
A fantastic plane.
I got to fly on it once from Capetown to Joburg to Frankfurt.
Peppy plane, and only 45 made and a handful left in flying condition.
Well in that end, the 747-300 had a place.
I remember those other versions of the 757. I think they should have made that platform a P-3 Orion replacement offering. It would have a lot more potential than the 737 based ideas.
I don't follow it all as much as I used to, and that is interesting about the 767-400. IMO the E-10 will most likely incorporate more than the glass cockpit. I like your idea on the GENx engine derivatives for these aircraft, but most likely that engine would be downsized a degree.