I don't think there needs to be a diplomatic effect of A-Bombs,since it never had in real life.No one blamed USA for using it,diplomaticly as far as i know.
On the other hand the IC and Leadership cost could be higher because you only spend 1 leadership point in your huge leadership pool when you're one of the major countries.It could be a multiple research project reaching to A-Bomb,just like in HoI1
On the other hand the IC and Leadership cost could be higher because you only spend 1 leadership point in your huge leadership pool when you're one of the major countries.It could be a multiple research project reaching to A-Bomb,just like in HoI1