Sorry but that isn't what this implies at all. This implies they're just now thinking about where to even take the second game, meaning that they haven't written the story yet.

Sounds they're looking into and have good reason to. It really comes down to how complete they feel they left the experience. We'll know within 2.5 years if a sequel is really happening.

That line about looking at all possibilities for a sequel has been said before by Naughty Dog.

They may have a small team working on establishing the basis of a second title, what part of what's left of humanity they want to explore, who the main character(s) will be, where they will go and why...

Are we going to fight those giraffes and those monkeys?

A new exclusive IP that's sold more than 7 million units? Yes, it's getting a squeal.

They're hardly going to say we've written out what we want for future stories, or something along those lines, because instead of 95% sure we'll be hundred percent sure.

Plus Bruce and Neil started working on the last of us a few months before Uncharted 3 shipped, they've now dedicated to a sort of two-team studio, so one set of people will need something to do.

After tlou shipped, there's about 8/9 month gap between then and when amy hennig left. So while bruce and neil weren't directly involved in u4, they had to do something, and that likely was jot down ideas and inspiration for the next game.
Trust me, the basic story of tlou2 is written by now.

They jotted down ideas or wrote the whole story? Which one?

I'm ok with a sequel, but I agree that Joel and Ellie shouldn't be in it. New characters on the rest of the planet are just begging to be revealed.

btw the last of us movie is gonna re-tell the last of us 1 game.

During the 8 months gap between tlou1 and amy hennig leaving would be the time they sit down and jot down the idea's they have for the next game where they want to go. That wouldn't be more than 5/6 months, depending on how pressured they would be. 

Now 11/12 months after tlou1, surely a base story is done with idea's of characters, setting, themes etc.

And the character artists who are now done with uncharted 4 since uncharted 4's story is done, will be balancing what's left on uncharted 4 and starting up working on the characters of tlou2.

Well, how about we all agree that Sony is not above milking their hit first party games, and that they are not all about new fresh games?

I expect it to go like this: UC4 -> New IP -> TLOU 2.