The issue right now isn't with loiter time or payload. Range is the enemy more than anything right now. We fight a global conflict and providing resources anywhere at anytime is alot harder than it sounds. Making A-10s into drones doesn't solve any particular problem. Once the Army fully realizes future vertical lift we'll have a better picture of what "local" CAS will look like moving forward. Right now we team 64s with UAVs all wholly owned and operated by the Army to project force locally.
Response time is key. An F-16 hauling ass from Al Udeid will give me more than an A-10 hauling ass from Al Udeid. Low risk precision is key. A UCAV at altitude raining hate in the from of hellfires presents very low risk to the asset and a great deal of precision for the troops on the ground. The A-10 can act great as a delivery platform, but it is slow and incredibly vulnerable. Time matters for those troops in contact, and providing fast precision is the key ingredient in CAS right now. Sustainment comes in the form of larger platforms such as the B-1 and the B-52. In a low to moderate risk environment you can start throwing in Army assets and special mission stuff like the AC-130. Air power is built as a stack, and the idea to to provide quick reaction to troops in contact with precision munitions. Bring in ISR platforms (or already have them in place) at altitude to develop the battlefield. Finally, sustain air power with larger platforms or locally employed assets (think short range long loiter) such as AH-64s, AH-6s, DAPS, etc.
The reason why the A-10 doesn't have a KEY role in all of this is because after decades at war, lessons were learned. Now the A-10 isn't SUPER BAD at CAS, we've just evolved. An F-35 will do the job just well in that it provides that critical speed, range, payload, precision and all with an amazing capability set. If we ever need to destroy battalions of tanks en-mass with zero risk of effective counter air or anti-air, I'm sure we'll see the A-10 again.
In terms of Khasham, you're also ignoring the dozen or so sorties flown that day by F-22s, F-15s, and B-52s that provided probably more than 80% of the total payload. Not to mention the many un-named ISR and UCAV platforms that probably stayed in the stack for the better part of that week. Going back to the "stack" mentioned above.