I'm not sure the savings in building "locally" in Japan are worth it, versus doubling down in China. The total market is 4~5M a year in Japan, a bit over 1M in South Korea. For it to make any sense they'd be targeting to build 1-2M for a given factory I would expect, and since they're unlikely to grab 20-40% of the domestic market (I'd be surprised if they hit 10% even with a smaller "Model 2"), this seems like it would rely on shipping cars anywhere - just like they would from South Korea (similar problems to Japan but even smaller domestic market), vs just adding on to China. Plus I'm not sure there's any available land of the right contiguous shape and size to build a GF in Japan or South Korea.
Even Australia would be mostly exporting if they built there (similar size domestic market to South Korea, looks like), but at least there's the advantage of plenty of land and locally sourced Lithium.
It probably makes more sense to keep adding factories in China to cover the rest of that region of the globe. New factories are probably going to be places like North and possibly Central/South America, the EU (possibly including the UK, if they can sort out the Brexit complications to vehicle production / exports), and maybe someplace like India (but they have lots of issues for foreign companies, etc).
If we're mostly concerned with "high availability" of factories via the method of "redundant governments" (i.e., trying not to put all eggs in one basket aka China), then I would pick Australia over South Korea or Japan any day of the week.