Engines,
Apologies, I obviously wasn't clear in what I wrote (making pesto and typing at the same time is not a good idea). I agree the current Harrier airframe can not be made to go supersonic. I was talking about a new airframe with some of the Harrier ideas used.
Personally I don't like the F-35 aircraft, but then I was not fond of the Tornado. That eventually became a good aircraft. I do believe that the F-35 will work.