In the page on Playstation.com, Uncharted 4 comes detailed as

Several years after his last adventure, retired fortune hunter, Nathan Drake, is forced back into the world of thieves. With the stakes much more personal, Drake embarks on a globe-trotting journey in pursuit of a historical conspiracy behind a fabled pirate treasure. His greatest adventure will test his physical limits, his resolve, and ultimately what he’s willing to sacrifice to save the ones he loves.

Source: https://www.playstation.com/en-us/games/uncharted-4-a-thiefs-end-ps4/

So he retired, and is in search of a pirate's treasure.

Any prediction on which treasure will be? Tell us your pirate predictions!

That's... for one thing pretty old, and also isn't really saying much of anything besides ''It's an Uncharted game''. It's all incredibly vague and is merely something to function as a brief overview. As for what treasure it could be, I think that would likely fit more inline with the other thread you made.

Uncharted 4 is likely going to appear at this Sony Event thing at least, and is rumoured to be playable even.

Yeah, but this time there is more information to go around predicting.

And now we can make a better prediction. And this information would be disregarded on my other thread.

That description reminds me oddly of Godfather 3.