As soon as tax incentive phaseout begins, it'll make sense to produce a large proportion of Model 3 for US customers during the following 15 to 18 months. I hope they'll deliver a lot of pre-phaseout cars to europe when they are still speeding up production thus postponing the begin of the phaseout so they can produce more cars during the phaseout period. However I think those pre-phaseout production adjustment deliveries will mostly go to canada because it's closer and early deliveries being closer to the factory seems to be Elon's plan.
That is a nice idea, but I doubt they will do that. If they did I suspect that most of them would go to Canada/Mexico..