If legends never die, then the North American P-51 Mustang is already immortal by all intents and purposes. But this doesn't mean Mustangs could maintain relevancy indefinitely in a military context.
Regarding your article “Small Arms” about the surge anticipated in sales of piloted turboprop military support aircraft, the Piper PA-48 Enforcer would be perfect for such a mission (AW&ST June 22, p.