My take is M3 will be made exclusively in US, while the MY will be made exclusively in China. Only time will tell.
The only vehicles I expect to be built in one location would be the "low volume" vehicles (S, X, perhaps 2020 Roadster and semi), while anything high volume (3, Y, Truck...) will be built in probably at least 3 locations if not more (at least one GF in US/Europe/China, possibly multiples per)
If you consider that there are not likely 12 unique vehicles to produce and there's roughly a dozen GF expected long term, they must produce at least some in multiple locations. S,X,3,Y,Roadster,Semi,Truck only gets you to 6, and even if you add some smaller cars below 3/Y that's at best two more vehicles. While every GF may not produce every high volume product, every GF starting with GF3 (Shanghai) should be expected to produce multiple high volume products.
I expect Shanghai will build 3, storage products, and eventually Y. I'm not sure if there's a large market for Truck in Asia, that may be a product only built in North America (since it will be low volume anywhere else). If they build smaller vehicles than 3/Y some day, then there's a market in at least some of Asia for that, I could see them built there too - but they might just build them at yet another GF someplace in Asia region.
I'd expect Truck to be built in at least 2 locations in North America, but only in North America (the low volume demand overseas can be simply shipped there like S/X). 3 and Y and anything smaller at 2-3 locations per region (NA/Europe/Asia), with likely such locations building all of the high volume products at each location.