I'm in favor of killing the A-10. It was built for one job: destroy the Russian Armor in the Fulda Gap, a threat that is greatly reduced.
For every other job, it's compromised. It's slow, can't handle high altitudes, or heat, or a high-threat environment. It doesn't offer anything beyond the big gun, a weapon that isn't always the right solution.
Big gun? Sure...and against a tank, it's a great weapon. Otherwise, a PGM is a better choice against nearly every other threat...and if it's a gun you need from a low/slow airplane, fire up the AC-130 and bring it in: more bullets, longer loiter, better precision.
Armored? Well, yeah, when you're using a gun, you're in range of every rifle on the ground. So, it was designed to protect the pilot from small arms fire. But it's a sitting duck against a fighter, and it can still be killed by SAMs, including MANPADS, which have gotten a lot better since this airplane was built.
I've fought an A-10 - like shooting fish in a barrel. Super-tight turn that's purely horizontal. He can't bring that gun to bear against a fighter, and can't get his nose on with a sidewinder (and carrying one of those reduces his bomb load). Sitting duck in a high threat environment, that's the A-10.
Lots of bombs? No, not really... and it can't take off with even a medium load and full fuel in a hot and or high location like Baghram. So, it needs longer runway (limiting where it can be based) and it drags the tankers down into the terrain and the threat envelope. In Afghanistan, the mountain peaks were higher than the A-10 refueling altitude, putting tankers at risk when there is weather. Putting tankers at risk is a quick way to lose the war. Tankers are critical.
Tough? No, not really. Kill it with an air-air weapon, including 20mm. Kill it with SAMs, including MANPADS. You've got to keep it out of high threat, even medium threat, environments. Environments that other airplanes operate in routinely.
Great CAS platform? Yes and no. The F-14s delivered more CAS than the A-10. Look, the troops loved seeing the A-10 because it was down with them, but other airplanes were delivering more ordnance, over more sorties, than the A-10. CAS, defined, is delivery of fires in close proximity to friendly forces requiring detailed integration and coordination. When the battlefield is spread out, like Afghanistan, the A-10 is often far away...and SLOW to support the troops. F-16, F/A-18, or better still, B-1 can get to where it's needed far faster.
You want a GREAT CAS platform? The B-1. LONG loiter, far longer than the A-10 without refueling. High speed dash to get to the target quickly. Huge bomb load. Better than a squadron of A-10s. Can be based out of theater, reducing the high/hot challenges and it tanks at high altitude, keeping the tankers safe.
The A-10 is a single-purpose airplane. When you look at potential future conflicts, most of them exclude the A-10. It's too slow, unable to protect itself, can't handle the climate or terrain.
Kill it. Pull the plug, now, and divert the $$ to something that can do the job across the range of potential conflict areas.
It costs hundreds of millions of dollars every year to keep an aircraft type in service. You have to have engine overhaul, airframe overhaul capability, avionics and weapon system repair capability, training for technicians and aircrews. That overhead exists, in basically the same size, whether you've got 500 airplanes, or a dozen.
So, kill the A-10, its mission can be done, better, in more environments, and in more potential conflicts, by newer, faster, more capable airplanes. Spend the overhead on buying more F-16s or F/A-18s. Airplanes that carry as many bombs, get there faster, aren't constrained by environmentals, or terrain, that don't put tankers at risk, that can defend themselves, and that are capable of multiple missions, like SEAD, OCA, DCA, Interdiction.
Don't waste resources at home, like overhead program costs, and don't waste resources forward, like deployment ramp space and logistic support on an airplane that does just one thing. If you fill up the ramps with an single-mission airplane that can't be shifted from one role to another as the conditions change, you've destroyed the essential flexibility of air power. You've put your entire campaign at risk.