I think it will be a launch title, whenever PS4 hits the market be it this year or early next. They have been releasing a new Uncharted every 2 years right? Also, we have heard about Naughty Dog expanding teams since Uncharted 3 released and shortly after the rumors of super high polygon count Drake. Sony is utilizing Naughty Dog extensively and they have probably been working with what was to evolve into PS4 hardware for the past 2 years. With their extent of assets, already established IP direction, and easier to develop on hardware, we are probably going to see Uncharted 4 at launch.
Sony wants to launch strong and Uncharted is their best IP to do that. They made sure to have an Uncharted on Vita for that reason but Naughty Dog themselves didn't work on it because they are busy on Uncharted 4 as well as another IP. (which I think will launch the following year as it takes longer to develop a new IP)
I honestly don't believe this to be an issue of discussion, but an almost determined reality. Sony will gear up their popular IPs for launch and then tackle new IPs after.
Before the PS3 everyone was nice to me :(
