How far gone are the A-10s at Davis-Monthan? My guess is they're probably all high-hour birds that've been sitting in the desert for years.Sure we could just knock 10 JSF off the order and then get 60 A-10 aircraft. However with the A-10 we could half the JSF order and have similar capability and save a bucket load of money in the initital purchase.
So you'd get a bunch of aircraft that you'd have to restore and modernize. You'd have to develop doctrine and train pilots. You'd have to develop a spares and support infrastructure. You'd have to buy munitions.
And they may not have much life left in them anyway.
Or, for $8 mil per new airframe, you could buy MQ-9 Reapers and get a vastly superior COIN and high-endurance sensor capability. And one that can even perform persistent CAS (though with even lower sortie rates than the A-10).
This would be a complementary capability to the JSFs, F-18s, F-111s, and Tigers planned or in service now.