Personally, I would love a Halo spinoff game
that allows us to command our own warship
with friends acting as the bridge crew.
It would ideally support VR play, but would
also be perfectly playable with a controller.
You'd play it in first person and you'd fill a
specific station on the ship's bridge while
one person filled the role of captain.
It would be really cool if it supported online
battles between ships commanded by other
players, but fighting Al would still be fun.
In a perfect world, it would allow you to use
alien ships as Elites or something, but UNSC
ships would be plenty for me to be happy.