Come on, he must be just kidding about the Nature paper...you're extremely lucky to get published in Nature as an academic full-stop, let alone as a first author in the middle of their PhD! Seriously though, I would say he isn't actually expecting that from you, and would be surprised that you have taken it seriously. Talk to him about the pressure you're feeling. If the results aren't going to happen by Jan, I'd make sure he know's asap, rather than the day before the meeting!