Note, it is the USAF that is supposedly looking for a COIN aircraft. What do they want it for and what do they want of it?
If they want it for use in low intensity operations such as central America then that would not seem unreasonable. If they are considering it for use in Afghanistan as an A10-lite then the requirement is different.
Do they want 'cheap'? Do they want 'rugged'? Do they want all weather and better capability etc?
Unless they tie the requirement down to austere and limited then the only real answer, for the USAF, is the A10.
The elephant in the room however is the US Army. They already have a versatile platform which, although it cannot carry bombs, is possibly more devastating than the A10. As Apache is Army that rules it out for the USAF but I don't see the USAF opting for 'cheap' when it comes to operating a COIN platform themselves.