I will list any related information here in this OP that refers to any discussion, interview or video that offers any insight into the question o which engine is to be used.
1 ) The first is from nowgamer.com via N4G and dated June 14 2011 and is a quote from Microsoft Game Studios corporate VP Spencer: Article
2 ) The next is a statement by Frank O'Conner and posted in CVG dated November 14 2011 and is a quote from E3: Article
3 ) This is again reported PCWorld on November 14 2011 as seen here: Article
4 ) This is an actual interview with Spike TV at E3 in Frank O'Conner's own words: Video
5 ) This is a video interview with Josh Holmes and Kiki Wolfkill by Game Informer dated October 26 2011. The key part referring to the engine takes place at 19:30 in the interview, but the entire interview is the best non stop back and forth discussion of the new game and the environment, music, sounds and the inclusion of more of the Halo history. The character of the Master Chief will also be more revealed to the fans as well. : Video
With all of this information it is still not completely clear what the actual engine is other than a culmination of engines. It is clear that it was stated, "343 obviously has partnered closely with Bungie for a while," Microsoft Game Studios corporate VP Spencer said, "We had been working with them on Halo: Reach and map packs. We started with the code base from Halo, so it's not something we had to re-roll from the beginning. [Chief Technology Officer] David Wu and the team behind the core engine tech inside of 343 have done a lot of work." Does this simply mean it will progress as in the past? Even by using part of the Reach engine, as well as others, would it be a completely new experience? Since being partnered with Bungie so early on, it would allow them to use just the code or writing they want minus, all the features of the current game, as they have done in the past by just bringing the best parts forward.
I hope this gives a clearer picture than some of the misinformation that I had even had.