yea they do but R&D and developing, optimizing engines take time. I have no doubt Amy and her team have story, characters, level designs etc all set in stone but, I just doubt the tech is there....
Going by two job listings posted on their site for a few months now it's started already i guess.
http://www.naughtydog.com/site/careers/graphics_programmer_ice/
http://www.naughtydog.com/site/careers/tools_programmer_ice/