Sorry for double post, but I was just thinking about something:
Our dear Stinklez brought up the fact that Halo 6 would be more iterative and fine tuning of Halo 5's sandbox. However, he stated that a while ago and now we are getting Halo without a number at the end and in a whole new engine. Also, Frank mentioned that they want the new Halo to be similar to the feeling of Halo CE where you are waking up to a whole new world and making the game a great entry point for new players into the series. Sounds like they are doing a soft reboot of sorts, especially if you look at the nice new art style partially on display in the new trailer.
I say all this to speculate: Perhaps 343 went back to the drawing board and will actually make it a more classic style game? Frank's comment on Halo 6 being more iterative could have been a genuine statement that is no longer valid due to internal changes.