We're not trying to "replace" the A-10. We're trying to find a COIN aircraft so that we can saturate the combat zone with air support. Personally, I'd go with a armored, militarized crop duster like the Air Tractor AT-802U:
Replace the hotshot fighter jocks with NCO pilots, saturate the skies with cheap COIN aircraft and kill the jihadis where ever we find them.
You can't kill them all, but the fear of attack is more powerful than the actual attack. You can't attack with silly looking planes that look like they were made in shop class. The Stuka is a perfect example.
