After rewatching the original E3 Trailer for Halo 5. It seems that the add was meant for Halo 6 and ill tell you two main reasons why.
In Halo 5 he got hit by Spartan Locke which is where the crack in his visor came from. Chiefs Visor is clearly shown in the trailer below having a crack in the screen which is clearly the aftermath of Locke. Master Chief is also looking for Cortana which we all know at the end of Halo 5 she controls a Guardian ship which just happens to be what he finds in this E3 2013 Trailer aswell.
Seems as if Halo 5 was a fill in story just to get Cortana in the ship and Master Chief battered and on the search. Sometimes a game/movie has to take the fat of the story so we could end up with an amazing ending. Seems thats what they might have done with Halo 5 so i am expecting big things from Halo 6.
Also more good news is that 343 come out and said there wont be any new playable characters, it will be all about the Chief.
Plus Split screen will be back in all future Halo games. (Old news)