Before taking this back to a JSF thread...
"Where they have achieved commonality is in two major cost drivers - avionics and engines."
The latter, we already had, with basically the same donk in F-16, F-15, F-14, U-2 and B-2. (And, nearly, F-18 and A-6F.)
Avionics could have been done - although most of the US had a bias towards an integrated approach, which was a hard way to go and has been somewhat overhauled by Moore's Law, which favors federated avionics: hence the Super Hornet's large bag of tricks today.
(Getting back on subject, it does seem the UK backed away from centralization after TSR.2.)
The final bit that would have made sense would have been a common tool-kit of subsystems, specs and standards, materials (including RAM) and processes.
And I would add "in hindsight" but I was saying that in 1998...