This could be the rumoured third-person prequel game, or not. One thing's for sure this would count as one of the two big E3 reveals from Microsoft, if you believe that rumour.
"A very good and anonymous source tells us that Halo 4 is already in full development over at Bungie. I wish to God She/He/It had more details to share but at this point all She/He/It can confirm for sure is that Halo 4 is an official project being developed by Bungie, at this very moment," .
It could even be related to the Peter Jackson project; sadly all informants to the Internet have been coming up empty for now. I guess we'll just have to sit and wait patiently till E3, or another burst survey pipe from Intellisponse - either’s good enough.