Pretty clear this is the end. Naughty Dog has abandoned successful franchises before and if they are done telling Nate's story (judging by trailer and title I think so) then it's time to give it a rest. I have no doubt this will be the best Uncharted yet as they want to send it out with a bang (they've gotten better with each iteration already). They are always willing to do new things and I think they can make basically anything great. Hell they've gone from platformers to third person adventure to horror they may as well go back to Jak now!