I just read a post on B.net that Ryan Payton quit 343I. That let to a search on Google(just to see who this guy was). Upon my investigation I stumbled on to this site http://www.gamereactor.dk/nyheder/85780/Ryan+Payton+forlader+Halo+4/ a highly respectable site. It is in Danish however, but there are some quotes in english. I will type them here.
“I had a great run at Microsoft… I don’t regreat one day of it. But after a few years, there came a point where I wasn’t creatively excited about the project anymore.”
“The Halo I wanted to build was fundamentally different and I don’t think I had built enough credibility to see such a crazy endeavor though”
What he states that he wanted to built a very different Halo it seams. But he quite because hes expectations were never really met. Which could indicate that the upcoming Halo is not very far from what we know. As Reach was. However this does not mean that no new features will be in Halo 4 just that it is not that different from what we know.
This is just speculation, but I thought that I would share this with you.