Not sure why the A-10 even needed 'modernization.' It's primary role in ground support and killing tanks which it does exceedingly well. A supersonic fighter isn't well-suited to providing ground support since a fighter's claim to fame doesn't take place that low or slow in the sky. A-10's a subsonic plane which can actually make out individuals on the ground so infinitely better suited for such operations.
Plus of course when you shoot an A-10 you just make it mad at you. Shoot an F-35 and it blows up.
The Marines don't need nor want the A-10. They use their Cobras for close CAS and it's backed up by the FA-18s. Of course, the Cobra is the absolute most manueverable aircraft in the skies. The AH-1 is still in production. For CAS, the Cobra even outshines the Apache. That Apache is extremely armored and armed but it lacks the manueverability of the Cobra. What the Army might do is learn from the Marines and start using the AH-64 for what it was orginally intended and that is support of the ground troops. We seem to overlook the Apache and the Cobra, both are better at CAS than the A-10 and much more survivable in todays world.
Pilot saves six Marines earning him the Distinguished Flying Cross with Valor
"Two sections of F-18 Super Hornet fighter jets responded to the Marines' request for close-air support but couldn't help them because they would not fly below the clouds covering the mountains below.
Shortly after, the Marines received word that two A-10 Warthogs, one flown by 1st Lt. Aaron Cavazos, penetrated the cloud cover and found a way into the tight valley. While the A-10s diverted surface fire to themselves by using overt lighting, they were able to identify friendly and enemy positions allowing the Marines time to develop a plan.
The Marines quickly moved out of the compound to an eight-foot wall north of their position while engaging the enemy who was as close as 10 feet away. As they pushed north from the wall under heavy enemy fire, they heard the sound of the 30mm guns in support of their movement as A-10s made the first of a series of low-angle gun runs closer than 50 meters away."
Theory's best kept in a classroom.