I’ll build two Japanese Industrials on the Mainland in one of two situations:
Most Likely - I expect a Kill Japan First allied strategy. Either because of National Advantages selected, or because of previous experience with the person or because of how Russia and England developed their turns or all of the above. In this case, I cannot expect to have transports and surface ships available for moving units from Mainland China to the Asian sea board, so the complexes are worth their weight in gold.
Least Likely - I plan to engage in a Kill America first strategy. Again, I won’t have transports and surface ships to protect them for long, so I’ll need the complexes eventually.