It's strange...I love the A-10, both its rugged design and its crazy anti-tank capability. Keep in mind that retirement plans for the beast are slated for 2028, and all plans to retire it sooner have been shot down. That's 52 years of service, which is a solid service lifetime.
But that said, I think there's a decent argument that can be made for phasing it out given current operational needs:
The A-10 was originally designed in the Vietnam-era as a close air support(CAS) aircraft for conventional wars, armed with a payload of unguided bombs and shells to destroy tanks.
Helicopters at the time couldn't carry these types of anti-armor heavy weapons, and strike aircraft like the A-1, A-6, and F-4 couldn't survive anti-aircraft fire at low enough altitudes to put their bombs on target. In CAS roles, missing the target meant killing friendlies, obviously unacceptable.
Thus, the A-10 was built like a beast so that it could survive SAM/AAA fire at the low-altitudes needed to deploy these weapons accurately.
Over time, however, CAS munitions have evolved with guidance, from missiles like the AGM-65 and Hellfire, to laser-guided (GBU-27) and GPS-guided (JDAM) bombs. These have longer ranges and thus don't require the carrier aircraft to be nearly as survivable. The A-10s resistance to AAA and small arms fire seems less relevant.
This suggests that the A-10 may be less necessary for strike roles, even if it carries them out admirably.
