To quote Chris on Era:
Expect something in line to the PS4 launch.
So, around 300K first week/400k first month despite releasing during the holiday season this time around (PS4 launched late February in Japan)? That's... quite low for a start. Hopefully, only the 300K first week is correct and it will sell more than 100K after that during launch month. Otherwise, PS5 is off to a real bad start already in Japan.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454