Devil's advocate in me wants to say this is merely the new-content-heavy repackaging of MGS4, just like you saw Substance follow MGS2 and Subsistence releasing not long after MGS3. The verbiage (Substance, Subsistence, Existence) is certainly similar enough. But then, there's no "4" anywhere in this new title, so could it be something entirely different? As Jeff and I agreed on a recent Bombcast, Konami ought to drop the "Solid" moniker now that Solid Snake's story is done, get back to the core Metal Gear franchise and start over with a new naming convention. But in the age of persistent marketing and eternal product branding, I fear the Metal Gear Solid name will live on in new products ad nauseam.
What do you think MGS Existence is? What would you want it to be?
UPDATE: Siliconera reports that Konami also registered "Existence" alone in the U.S. on August 11.
But then, some attentive readers in the comments pointed out that Existence is also the name of the bonus DVD included with Subsistence, as confirmed in this quote from Wikipedia.
"Limited Edition" copies of Subsistence also include Existence, the game's cut scenes edited into a three-and-a-half-hour feature film with additional scenes and remastered sound.
The plot thins? Doesn't explain why these trademarks were just now registered, though; I'm still betting on something new. Or at least hoping.