Cortana is my favorite character in the Halo series.
Which is why I’ve been thinking lately:
What about a Cortana spin-off game?
It would be a Choose Your Own Adventure game like, for example, Life is Strange.
It would take place before the events of Halo: Combat Evolved and deal with Cortana using her abilities as an AI to travel near-instantaneously to computer systems on ships, planets, and (in the case of Master Chief) Spartan armor as she attempts to make the galaxy better (or worse) for humans fighting the Covenant.
This would open up Halo to a new audience. An audience that might look at first-person shooters with distaste, or might enjoy playing as a woman and not a man.
There is also the possibility for further brand extension: Life is Strange to Become Live-Action TV Show
Just something to think about.