To date, we've gotten tons of clues that The Last of Us 2 is being worked on. At this point we are just waiting for official word, which I'm going to hazard a guess, will be at PlayStation Experience. Failing that, next E3.
The other night though, we got something else, I'm going to throw onto the clue pile. In a stream writer on Uncharted 4, Josh Scherr, appears to have slipped up, referring to a sequel by repeatedly saying 'the first Last of Us." You can see it play out in this video (via gamepur):
Honestly, I don't know how solidly you could take this as a 'confirmation' of The Last of Us 2, but it certainly can hang with all the other clues we've heard. They certainly are beginning to build up, there is no doubt about that.