We already have a select collection of games given to us by the original article's author as to what the game is.

http://www.psxextreme.com/ps3-news/4796.html

http://www.psxextreme.com/ps3-news/5705.html

Ben Dutka stated in the first article's comments hours after it was posted that the game in question had already been mentioned in the comments section.

Twisted Metal
Metal Gear Solid 5
Trico
Halo 4
Ratchet & Clank Future 2
Warhawk 2
Grand Theft Auto V
Dance Dance Revolution
Jak & Daxter
Sly Cooper
Final Fantasy VII
Heavenly Sword 2
Syphon Filter
The Getaway
New Rockstar Game
Onimusha 5
Bushido Blade 3
Mega Man
Earthworm Jim
Hitman 5
DarkStalkers
Battletoads
Breath of Fire V
Colony Wars
Kingdom Hearts III
Final Fantasy X-2
Suikoden VI
Resistance 3
Killzone 3
Gears of War 3

There's a collection of every officially unannounced game posted in the comments prior to Ben's post. Obviously Halo 4 and Gears of War 3 are borderline impossible so those can be disregarded. Ben went on to confirm that the game in question was not Team ICO's next project, a Final Fantasy X-2 remake, and Battletoads in the comments of the two articles as well as Kingdom Hearts III on the site's twitter page. Lastly, Ratchet & Clank Future: A Crack in Time, Metal Gear Solid: Peace Walker/Metal Gear Solid: Rising, and Agent were all officially announced at GDC and E3 so none of them can any longer be the "true-blue system seller."

Now that we've weeded out the deconfirmed and the impossibilities we can narrow it down further with informed speculation. First of all, let's establish what in the author's opinion is a "system-seller." The orginal article was one created to point out all of the PS3's greatest system sellers both released and upcoming. The games included in that list were Metal Gear Solid 4: Guns of the Patriots, LittleBigPlanet, Uncharted: Drake's Fortune, Killzone 2, Gran Turismo 5, God of War III, Uncharted 2: Among Thieves, and the currently unannounced game in question. The author also went on to point out to questions in the comments section by readers in regards to the absences of certain games that he didn't consider Resistance: Fall of Man, Resistance 2, inFamous, White Knight Chronicles, or Final Fantasy Versus XIII system sellers. Knowing this, we can confidently throw out certain possibilites such as Dance Dance Revolution, Bushido Blade 3, Mega Man, Earthworm Jim, DarkStalkers, and Colony Wars. I think I can speak for most when I say that no matter how good most of the above games may be, none of them are likely to come anywhere near the list of games Ben doesn't consider to be system sellers, much less the ones he does. That takes us down to 15 possibilites.

Now let's narrow down the possibilites more. Timewise, it really isn't supremely realistic to expect that Killzone 3, a new Jak & Daxter, or Sly Cooper by Guerrilla Games, Naughty Dog, and Sucker Punch Productions respectively would be ready for a 2010 release given the typical development periods those studios have. Less than a week after Ben published the original article did he publish a second article about how the PS3 did not need a Final Fantasy VII remake so it's easy to speculate that it couldn't be that. It would extremely odd for Ben to consider The Getaway an unannounced game considering that it was officially announced previously and then cancelled. Finally, given the revelation that it is Sony's decision when the game is announced in the most recent article, it can confidently be believed that the game is in fact being published by Sony. If that's true, Grand Theft Auto V, Onimusha 5, Hitman 5, Breath of Fire V, and Suikoden VI are unlikely. With all this, we've narrowed it down to 5 good possibilites.

Twisted Metal
Warhawk 2
Heavenly Sword 2
Syphon Filter
Resistance 3