Now, this is just an idea so please take this lightly and not seriously.
I was watching the new Star Trek and thought of how Halo 5 should open (no clue why I was thinking like this).
The scene should be like this: Master Chief at the memorial that was shown at the end of Halo 3 and someone comes up to talk to him (Lasky would be cool in this one; and talking about what happened in Spartan Ops) about the war that happened and what he will do next. Then, something happens; such as, finding a signal that could be the Didact or the Didact attacks Earth again.
I do not know exactly what, but if this sounds like a cool idea just let me know. I just thought I would get this out there so people can start thinking of what Halo 5 might have in it. I know I am looking forward to the game. Again, I was just thinking about what I would like to see.