PS4 is really suffering in Japan. I expect these weekly Japanese updates to be all about the Switch for years. I don't see anything coming around as a serious competitor in Japan.
Switch sales in Japan will overtake the 3DS... and the 3DS even outsold the PS2 in Japan. So yeah, it doesn't really matter what Sony has in store with the PS5, it's not going to come close sales-wise in Japan. Switch will dominate the charts in Japan probably for the next 3 years.
LTD: PS4 - 125m, Switch - 110m, XBO - 51m
2020: PS4 - 9m, Switch - 22.5m, XBO - 2.5m, PS5 - 4.5m, XBX - 2.8m