These are the amount of games to sell over a million copies in Japan for the previous Sony consoles according to VGChartz.

PS1 - 30
PS2 - 20
PS3 - 2

How many do you predict for the PS4?

One.

Final Fantasy XV.

FINAL FANTASY 15

FINAL FANTASY 7 REMAKE

YAKUZA

RESIDENT EVIL

GRAND THEFT AUTO 6

KINGDOM HEARTS 3

GRAN TURISMO 7

DRAGON QUEST

METAL GEAR SOLID PHANTOM PAIN

METAL GEAR SOLID 1 REMAKE(if it happens)

STAR OCEAN(depends how good the game is and how SONY markets the game)

CRASH BANDICOOT(if SONY and ACTIVISION bring it back)

TEKKEN(if the game can be brought back to its greatness and how SONY markets it)

JUST DANCE(if made PS4 exlcusive and marketed well and good game)

PARASITE EVE(if big budget and brought back in a big way)

STREET FIGHTER(depends how SONY markets the game)

SHENMUE 3(depends how SONY markets the game)

CALL OF DUTY(depends how SONY markets the game)

MONSTER HUNTER(if a full-fledged game is released)

HORIZON(if Japanese gamers like it as they like mech games and monster hunting games)

ONE PIECE(depening how the game is)

HOT SHOTS GOLF(depending how good the game is)

DRAGON'S DOGMA(depends how good the game is)

DYNASTY WARRIORS(depends how good the game is)

Uhhhhhhhhh.
I guess 2. Final Fantasy XV and Resident Evil 7. The latter may be difficult, though.

Grand Theft Auto VI.

Metal Gear never sold 1 million in Japan. Not even on PS2. And PS4 is going to sell just more than 1/4 of PS2 lifetime in Japan.

How can Metal Gear PP sell 1 million?

PS4 can easily sell 10 million console so thats half or 1/2 PS2 sales

and METAL GEAR is one of the most legendary and elite franchises and a big japanese franchise also.And most of all today marketing and hype can send a game much much higher than in the past and people just grab consoles for this.

METAL GEAR can easily make past 1 million plus the LIMITED EDITION PS4's will drive even more sales

Well, if you say "easy".....

Currently the only announced game that will do it for sure is FF XV

FF VII Remake has a shot, but I'd say it's not guaranteed. Same for KH3.

If FF XVI comes to PS4 and is a standard JRPG then that should do it as well.

If DQ XI goes to PS4 and is a standard JRPG then that's a guaranteed millionseller.

Resident Evil 7 might do it, don't think GT7 will do it.

What else... GTA 6 is a pretty good candidate as well, if the series growth continues.

Everything else would be out of the leftfield I'd say.

I'll predict a fancy 4-5.

Ehh...  THE LAST GUARDIAN?