The Congressional Budget Office (CBO) report in May 2009 "Alternatives for modernizing U.S. Fighter forces" grapples with options should, basically, the Joint Strike fighter (JSF) or F-35 program be cancelled.
Interestingly the report makes the point that US Marine Corp concerns about the 2018 in-service date slippage for their own AV-8B Harrier replacement, "instead of being retired as F-35's are delivered to the Marine Corps, AV-8B's would be retained as long as they are flight-worthy" (page XIII). This is in contrast to the United Kingdom, whom as part of the outcome of a recent, resources-led review decided to scrap the Harrier capability ahead of the introduction of a new generation aircraft carrier.
US Marine Corps plans are all based on retaining the AV-8B Harrier through 9,500 airframe hours (page 10).
The report then makes the killer blow (on page 13), "The Marine Corps AV-8B's were purchased (or remanufactured and upgraded) more recently than many F/A-18 A/B/C/D's of more modern design and, hence, have substantial remaining service life"
One of the big alternatives touted in UK circles to the JSF or navalised Eurofighter typhoon is the F-18 Hornet (which would be bought from the US). Why on earth does the RN not lease or buy some of the US aircraft and fly them until they reach the limit of serviceability ?
For the USMC with the resources they can consider the Harrier as obsolete on the modern battlefield. However many of the scenarios for which the is organising would be 'lower intensity' by definition - for which aproven airframe like Harrier is an essential force multiplier.
Alternatively, as was already suggested in 2007, why not manufacture new Harriers under licence in India ? BAE Systems are seeking to carve out a niche in the emerging Indian defence market and US is deploying the President on a major tour (which must chafe the FCO)...