LO,
Thanks once again for coming back.
The projects I'm referring to were A/F-X, NATF, MRF (yes, single seat, but a large and expensive twin engined design), AX, and not forgetting the A-12. I can confirm that around the time JAST was being developed as a programme, there was real concern in some US quarters that the DoD was becoming institutionally incapable of executing a tactical combat aircraft programme (their words, not mine). Yes, the Navy were really unhappy about going for a single engined design, but don't forget that the USAF had already driven through a large twin engined solution for F-22, and were happy to accept JSF as the 'low end' part of a future combo. In the event, they had to accept that the original '1000 aircraft' F-22 programme was simply unaffordable.
You are, as usual, right on target about the early years, when the JSF mantra was 'commonality and high production rates' - although many of us were less convinced about the need to build one aircraft a day as opposed to say. one every 48 hours.
It's absolutely true that the need to drive weight out (of all three variants, by the way) has reduced the amount of commonality in the airframe area. (Although they are still able to use 'cousin' parts that are machined from common billets and forgings).Where they have achieved commonality is in two major cost drivers - avionics and engines. That will work in their favour going forward.
As ever, best regards to those actually working their rear ends off to deliver the capability to the people out there doing the hard stuff,
Engines