Now that we've seen The Last Of Us , we think this question is well worth asking.
There are several points to consider: firstly, Sony has said they don't want to be second to market again this generation. So if we go along with rumors that the new Xbox will launch at the end of 2012 (or not much after), we'd like to assume the PlayStation 4 wouldn't be far behind. Secondly, take a look at some of the current trends in the industry among very successful developers and publishers:
Annualization has become a definite part of the industry; Call of Duty and Assassin's Creed are a couple examples, and we'll probably see more of it in the future. The bottom line is that a publisher would love to have one massive blockbuster every year. This requires expansion beyond the accepted, or that one gigantic recurring IP your company has always counted on; Take-Two Interactive should be noticed. It used to be only Grand Theft Auto but by turning Red Dead into a gargantuan series with Redemption , they've got a double-barreled attack for the future.
As for Naughty Dog, there's little to no chance that Uncharted will be left behind. Sony just can't afford to let that happen. There's this new IP, The Last Of Us , which may launch at the end of next year, which may mean Uncharted 4 will release the following year. One hugely successful, critically acclaimed title per year, right? It would work out nicely. And if we're approaching the new generation and Uncharted 4 is slated to launch in late 2013, wouldn't that make it a title for the fancy new PlayStation? Perhaps even a PS4 launch title?
This is all speculation, of course. The Last Of Us might be further off than we think, or maybe with two separate teams currently working at Naughty Dog, the studio could produce both their new IP and the fourth Uncharted within a relatively short span of time. Still, let's not forget those rumors about "at least one internal Sony studio" working on PS4 concepts…what better studio to attempt this than Naughty Dog? And what better series to bolster the launch of the PS4?