Actually, this happens already: when a Model S/X is sold in China, the cell was made in Japan, shipped to
Nevada, assembled into a battery pack, mated in Fremont and the shipped back over the Pacific to China.
Shipping 2170 cells would be pretty cost efficient, as they are dense and can be packed tightly.
Also, the primary short term goal would be to avoid the 40% tariffs, shipping a full car costs maybe $1,500, cell shipments would be significantly cheaper.
Once the Shanghai cell lines are up and running they could substitute.
Edit: correction by
@Artful Dodger.