Regarding PS4, I wonder if it's that Japan aren't interested in it at that price point any more, or if they're just no longer interested in as a system any more.
I've been wondering the same thing as well. I can see both scenarios as likely. It is very likely that Sony cuts the price and then sales become much healthier. On the other hand here is the other scenario. Often when a successor console is released the previous console sees a huge drop in sales. Well, in Japan they may not see the PS5 as the successor to the PS4. Instead the Switch is going to be the dominant console for the next few years (home and handheld), so it effectively becomes the successor to the PS4.
The only way to really know which is true is for them to give PS4 a permanent price cut in Japan, and then see what happens.