If there isn't a PS4 port in Japan, there's not going to be one here.
Relegating the series to digital only isn't going to make the series any bigger.
It seems some games have gotten PS4 versions or will get PS4 versions specifically for international release, the new Godzilla game for instance was only announced for Japan on PS3, then with the localization announcement had a PS4 announced too, not even sure that's coming out in Japan along with the PS3 version.
Not that such a thing is particularly likely though, and part of the going digital angle may also be they've given up hope on expanding the series so may as well serve the existing base as cheaply as they can at least. Retailers may not even WANT to stock newer entries given that they got deep discounts, Dead Souls I got only because I saw it for about $10 (probably less!) at Big Lots.