Obviously, it would be called that, but for anyone who doubted even the slightest, bruce strayleys twitter bio says

Game Director Dude at Naughty Dog on#TheLastofUs and #Uncharted 2 & 4. Art Director of U1. It's gonna be awesome... Ship it!

https://twitter.com/bruce_straley

As of 02/06/14 22:00bst

pls be excited for uncharted

keeping numbers = MOARR SALESSS

It that a surprise ?

Well kinda, killzone shadow fall, infamous second son, seemed like uncharted was gonna follow the subtitle number less thingy too

Well first people thought it wouldn't feature Nathan Drake. Then they thought that it would be totally different because of lay offs and that Nathan could be in it but that the game would take such a different style that it wouldn't be called U4. Then they thought it would be a lot like the last of us with a mature Nathan Drake. So everything that gets confirmed is a surprise for the internetz! Wonder what people think now that slowly a lot of details emerge and get confirmed

It is about Nathan Drake and his team and the game is called Uncharted 4. But I assume there will be a subtitle attached to it. 

Something tells me Sully is going to die in this game, no good significant person has really died in u4 :(

Glad Straley and Druckmann are on the project, best dynamic duo in the industry. But on the other hand, the second project starts without them at helm and while I hope it's TLoU 2, I don't trust anyone else with the franchise other than them :-/
Was there any co-game director/co-creative director on TLoU?

I was hoping that they would go for Uncharted 5. So, they can directly compete with Halo 5. Oh well, 4 it is.

How original

If they wanted to do that it woulda been called Uncharted One

I kid XD