Easy answer. Let's say you kept the 30mm gun. Now, put an X
second delay in the controlling of the gun with the pilot
(operator) somewhere not within a few hundred miles. Now, go in
as close as an A-10 does with it's human pilot onboard. Now,
fire that gun. It's bad enough with the accidents that the A-10
with it's human, real time, pilot can do to friendlies. But take
him out of the seat and you are just courting with dozens killed
from a mistake. It's too lethal.
All of the other weapons are already carried by cheaper, longer
duration UCAVs. Remember, the A-10 is a 14 million buck (1978
dollars) bird and you can part it out for more than a standard
UCAV when you factor in the cost of modifying it. Dollar for
dollar, it's a stupid idea by someone trying to extend the A-10
past it's need cycle.