They're making The Last of Us.
Uncharted is their bread and butter. It makes them a lot of money. This isn't the Naughty Dog of the PS1 / PS2 era. They're not going to abandon Uncharted just because it's the start of a new gen.
That might be but I still would like to see them move on completely. I feel that UC was a great move away from Jak and an opportunity to explore new technologies and design concepts without being tied to the tropes of an established IP. The Last of Us is going to be interesting because it will be released so near the end of the generation. It would have made more sense for UC4 to come out this year and then The Last of Us to be a "launch window" release for the PS4.
ND is very talented, and if they think Drake still has more story to tell then so be it. However, I found it very difficult to suspend my disbelief in UC3 as Drake went from one impossible luck based scenario to the next. I enjoyed UC1 and 2 Drake because the majority of the time things were quite grounded (not always, very true, but most of the time) within the reasonable limits of human physiology and probability. I also don't really feel like UC3 developed the characters in any significant way so it left the impression that the universe was played out. Thus I fear that a new entry would come across as an empty (safe) cash grab.
I would love to see a return to the more dynamic design of UC2 and the multiplayer of UC2 Beta, but I think those days are long gone.