Switch is already the 5th highest selling system of all time in Japan and is coming up fast on #4 (PS2) and #3. (3DS) It's basically guaranteed to be at least the third highest selling ever there in lifetime sales.
By contrast, while PS1 and PS2 both sold over 20 million in Japan, PS3 dropped to just over 10 million, and PS4 is going to fall short of that again, having stalled out at a little over 9 million. The big question now is whether PS5 will continue this decline. It was tracking ahead of PS4, but at this rate it should soon fall behind it.