As usual with Sony products in Japan, I expect the limit to be on the supply side rather than demand in the first few months. I gotta imagine the massive, massive bulk of PS5s will be going to North America and Europe, with Japan and the Rest of the World left to put whatever scraps are there on the shelves.
Sony can't even manage to keep a healthy stock of PS4s in Japan right now. There's no chance that they'll be able to handle to the demand for the PS5 there for quite some time.