The challenge Sony will face in Japan ist that in a few years its only viable console will be the PS5. We often compare PS3 and PS4 to potential PS5 sales, but Sony had a very successful handheld during the PS3 era and a moderately successful handheld during the PS4 era. In the past, there were always multiple Sony systems for Japanese developers to do cross platform releases on. Devs could release a game on PS3 + PSP, or PS4 + Vita, or even on PS3 + PS4 + Vita for example. But in less than two years, Sony's whole Japanese install base will consist solely of PS5 and thus be lower than 5m probably.
I expect many Japanese third party developers to cling to the PS5 as long as possible, but in the end it'll be harder than ever for them to release Playstation exclusive games.
Essay Pro