Good post Swordfish, exactly what shaped my "hunch." I also believe Amazon was saved a lot last year by Switch being sold out for long periods. I'm not sure that will be the case so often this year if Nintendo have plans and production in place to reach their 20m shipment goal.
Depending on pricing and deals I expect a close fight in the US this year. Outside of the worldwide big picture. I'm thinking a close year anyway of maybe 19m NSW, 18m PS4. Roll on the rest of the year.