Once the assembly line is established in Mobile, the tax treatment will be exactly the same as for A320s and A321s already assembled there so the financial and legal aspects are already well understood. Actual manufacturing jobs will likely stay in Canada and N Ireland provided those are efficient plants - and they will now have Airbus's know-how to ensure that they are. With Airbus's supply-chain power and a ramp-up in production as a result of increased sales which the Airbus link will bring, production costs will fall. The prospects for this aircraft family are transformed by this development and the ramifications for Airbus and Boeing are enormous.
Watch for Boeing to raise anti-trust issues - their last hope!