Was the USAF still interested in the Mustang in 1980?

The idea of continuing to use the Mustang long after World War II did not come from Piper. The Enforcer concept was born and first flew as the Cavalier Mustang, the work of David Lindsay, owner of Cavalier Aircraft, as a response to the US Air Force's PAVE COIN program. In other words, it was about offering a refurbished piston fighter for light attack missions, at a time when the jet dominated the inventory.

The aircraft was tested with favorable results in 1971 and 1972, and despite that it secured no contract with the USAF. That first attempt thus remained a technical demonstration without commercial follow-through: the Air Force tested the formula, assessed it positively, and did not buy it.

The story reopened the following decade. In 1984, with a $12 million allocation approved by Congress, Piper built two new Enforcers, designated PA-48. The aircraft were evaluated by the USAF, but with a telling detail about the customer's level of commitment: only Piper test pilots flew them. Once the evaluation was complete, the Air Force again decided not to acquire the aircraft. So, answering the substance of the question, around 1980 the Mustang was still on the table as a basis for a light attack aircraft, with public money behind it and an official evaluation campaign, but the interest never translated into an order on either occasion, neither in the early seventies nor in the mid-eighties.