Although unreliable IMO since he was not accurate about name changes last year, Tidux has tweeted, saying he has heard Coop is a feature in Uncharted 4.

So, what im hearing a lot. It's Co-op #Uncharted4

— Tidux (@Tidux) April 6, 2016

My question to you is; Will you be playing as Nathan and Sam through the story mode or will it be a stand alone coop mode?

I'm pretty sure there's no main campaign co-op. But I don't rule out a secondary co-op campaign, like the ones in Uncharted 2 and 3.

Wether it's main story Co Op or not, as long as there is Co Op, it's pretty neat tbh

Would be awesome to have it... but i do doubt it. I would dare say whats said above by Wright.
All i know is cant god damn wait!!

The way he phrases it alludes to it being the campaign. The whole brother scenario also seems to fit too well not to....

But it certainly could be the classic way the did it before. 

I would personally not like to play through the game in coop as my first experience.... I take Uncharted story as a totally personal experience. After the first playthrough could be good to mix it up. But we will see....

If there was coop in the campaign wed have heard about it already, this is not something ND wouldn't be talking about. Theres probably coop on the multiplayer modes tough.

According to Giantbomb coop MP has already been confirmed http://www.giantbomb.com/uncharted-4-a-thiefs-end/3030-44507/

I am always down for co-op campaign!

I doubt there is co-op campaign. That would be a selling point, they would have already mentioned.

a secondary co-op campaign, a la uncharted 3 MP, possibly. I don't know about the actual ones, sounds kinda restrictive.