I'd recently been reading some (to a newbie) well argued cases for maintaining the A10 fleet further - not just because of the delays with the F35 but because we may be entering another cold war, which is just what the A10 was originally designed for. Really close support with cannon may be safer for friendly troops than missiles or bombs (or not, I don't know). Also, low level armed recon in poor weather is something that it can do better than any other jet.
It's getting off topic somewhat, however, but I wonder if a combination of new air superiority stealth fighters and a more modern dedicated strike aircraft might not have been cheaper and more effective than the current "everyone can do a bit of everything" approach...
From a pet rock perspective, though, I'd love to see A10's in the RAAF.
The design of the GBU-39 Small Diameter Bomb is specifically aimed at increasing effective payloads of precision guided munitions while minimising collateral damage, particularly the Focused Lethality Munition variant. I wouldn't be at all surprised to find it safer for nearby ground units than a strafing run from an A-10. Your gun run is going to be subject to at least some dispersion and the concept of "danger close" relative to a cannon the size of the GAU-8 would be no laughing matter...
While the F-35 program has had issues arising from its attempt to engineer three disparate variants into a single airframe, there is ample evidence that modern multirole fighters can indeed "do a bit of everything". If you look at most 4th generation US airframes, the trend has been towards expanding capabilities to fill multiple war-fighting roles. The proliferation of smaller, more accurate and more numerous munitions only serves to expand the air-to-ground capability further.
As GF rightly points out it has actually been strategic platforms that have served the CAS role most effectively in places like Afghanistan - they can not only carry substantially larger amounts of munitions than tactical platforms, they can match their payload in endurance due to massive fuel reserves, and the new generation of guided weapons means they aren't limited to littering an area with rackfuls of dumb bombs.
There's a pattern in guided munitions at the moment where they are increasingly being miniaturised. This follows several trends - a desire to arm small UAVs, the ability to engage targets very specifically within counter-insurgency conditions where civilian targets are likely to be nearby, and making use of this increased precision to allow a smaller warhead to achieve a similar effect to larger previous generation weapons. Take a look at the Viper Strike glide bomb or AGM-176 Griffin missile. Both of these weapons are even smaller than the GBU-39 mentioned above and are being integrated into close air support variants of the C-130, along with the Hellfire missile and SDB. If you have a look on youtube you'll find some videos of Viper Strike testing - the weapon is sufficiently focused in effect to blow up the occupants of a car with minimal collateral effect outside of the vehicle chassis. These are the chosen replacements of the 25mm rotary cannon, 40mm Bofors gun and 105mm howitzer of the earlier AC-130 variants. While a 30mm Bushmaster cannon is retained, the trend is quite clearly towards precision targeted effects over sheer broadside power.
In effect these small munitions afford larger payloads for tactical and selected strategic platforms while also enabling more distributed deployment of the weapons - such as onboard UAVs and less conventional CAS platforms like the C-130. With their increased precision, weapon effects on target are more lethal while also limiting the danger of fratricides amongst ground units. Compared to this, the A-10 is just a machine of a different era, limited to weapons that are larger and/or less accurate than their modern counterparts. Given its specialised role, the altitudes at which it operates (and its correspondingly greater risk from MANPADS or even radar-directed gunnery), and with its precision limited by its payload, it's hard to envision a situation in which the overall benefit would be worth the investment cost. Particularly when the USAF wishes to divest itself of airframes - no air force of the RAAF's size wants to be caught out operating an orphan platform if it can help it; it already got a taste of that with the F-111, and I suspect there is zero desire to repeat the experience...
