As others have said, the A-26 was much more than just an upgraded A-20, it was a totally new aircraft. Apart from the better performance, heavier bombload and up to fourteen half inch forward facing guns its other advantage over the A-20 was the turret system. The rear gunner had a remote sight system similar to the B-29's. He could track an attacking enemy plane with his gunsight and the system would compute a firing solution and feed it to the remote upper and lower turrets. If the enemy dipped below the fuselage a lower periscope view would automatically be displayed in his sight so he could maintain contact.
This remote system ought to make the turrets more accurate if implemented in AH and would give coverage below the plane, unlike on the A-20. (Yes I know, the missing tunnel gun). But it would require new FE code to be written to support it. I guess we will see an A-26 at around the same time we get a B-29 since that would require the same sort of code. As for it being uber, just make it a perked aircraft like the B-29 would undoubtedly be.
