Well, the A10 airframes are getting pretty damn old, and low-altitude flight is murder on the airframe. Worse, it's not like we can re-open the assembly line and make more, the tooling was destroyed back about 1994.
Another issue is that the A10 is relatively underpowered, it can carry more weight in bombs than it has engine thrust. So a truly upgraded A10 would need new engines.
*I* would recommend to the USAF that they need to make a low-intensity COIN aircraft and then a high-intensity CAS bird. The CAS bird would be the replacement for the A10. My requirements for the CAS bird would be more survivable than an A10, at least as well armed as an A10, and better flight performance than an A10. I still think it'd end up looking a lot like an A10, but probably with bigger engine pods. I'd want to go all the way to CFM56s (same engines as on 737s), but those are huge and about 4x the weight of the TF34s used by the A10. I don't think it would be very likely for the CAS bird to be sold to other countries, but it'd be good if it was. Bigger production runs make for cheaper aircraft!
The COIN bird would be something else. I'd want to build it using as many off-the-shelf components as possible, and I'd start with the engine and prop off a C130 (either the old T56 or the new AE2100 from the -J models). That huge prop pretty much requires a pair of gull wings to get enough ground clearance. I'd also use an A10-style twin tail. The inboard section of the flaps would be blown by the engine exhaust, though that's mostly as an IR-suppression system. It'd have drooping ailerons, too, for better low-speed handling and shorter takeoffs. I'd also want to install a radar and an optical sensor pack. It'd be designed to carry at least 10,000lbs of ordnance under the wings, plus have 2x 30mm cannon in the wings (either M230 chain guns like the Apache or Mk44 Bushmaster II) and 2x GAU19 .50cal gatlings. I'd make it a 2-seat aircraft, probably using F18D canopy pieces. The back seat would have a drone control station, in addition to being able to look around and have control of the onboard sensors. With that much power, it should have similar performance to an F4U Corsair, top speed of at least 450kts.
The reason for the dual engine options is so that it can be sold to pretty much every nation on the planet with the old T56, while the US version runs on the newer AE2100. Smaller nations running the old C130s would obviously want the T56-powered version, while the US is phasing T56s out of service. Again, the reason for international sales of the COIN bird is to get the unit price down to a minimum.
