China is drunk on its own power. It is forcing Japan, Australia, the Philipines and even Vietnam toward a common purpose, namely, checking Chinese power in the region. If I were China, I would not want to see a militarized Japan.
China's expansion can only be checked if there is a balance of credible military forces in the region at least equal to or greater than that of China's. China stands to gain as long as Japan and all the other players in the region are weak. I agree 100% that China would not want to see a militarized Japan. That scenario would put their expansion in "check" and China at this time does not wish to be quarantined, to say the least.
Mark my words; China's claims do NOT end with Taiwan.
We are already seeing that in the case of the Senkakus, for example, and even with respect to their encroaching on their neighbor's fishing rights. China will continue to keep "pushing the envelope" until met with resistance.
Taiwan had better buy those 8 subs ASAP (for starters) and Japan had better have comprehensive, meaningful dialogue with the security stakeholders in the region soon. Time is running out.