Update 2 (25-2-2015):
So get this, the number 2 was related to Rising after all! See, we’re not crazy. However, it was created for this artwork to celebrate Metal Gear Rising’s second anniversary (which was last Friday to be exact).
Still, it is a bit strange that it appeared in a PlayStation 4 montage at a game show. And look at the artwork’s caption (translated by IGN): “Congratulations on the second anniversary. After two-years, I wonder what Raiden is up to now?”
Make of it what you will. Either way, we have a cool new artwork.
Source: Platinum Games Blog, IGN
Update: The rumor has been debunked
Aside from Chinese localization, nothing major has been announced at the Taipei Game Show regarding Metal Gear. Although…
During a montage showing off various PlayStation 4 games, we can hear sound clip of a character counting down. Just as he says ‘2’, a shiny metallic number briefly appears. Its typography is very much like the one used for Metal Gear Rising: Revengeance.
Kojima did say in 2012 that a sequel to the game would be possible, and that he would like to work with Platinum Games again, the developers who made the first installment.
If this is indeed pointing towards a sequel to Rising, it would probably mean it’s being developed for the PlayStation 4 (and likely other platforms as well). But keep in mind that this is just a rumor as of now.
Source: Taipei Game Show (around 1:39 in video)