Halo needs a skull that mimics the end of halo reach that the cracks get worse every mission you beat. 
  
What I would want in halo 5: 
Dual wield 
Energy sword bayonet 
Brute shot 
Hijackable scarabs 
New* plasma cover gun dropped by hunters. Covers target with plasma and takes away shields or the hunters join the unsc because the Covenant have lied to them.  
Keep the prometheans  
The prometheans joined up with the covenant 
Portal 2 testing room Easter egg 
  
Story:  The UNSC come back to reach to find out what was left after the war. Slowly, the master chief finds the sword base, New Alexandria, a pelican crashed into a scarab, Kat's body, and finally, the place where Noble 6 made his last stand. Master chief finds noble 6's helmet and that is when the arbiter makes his first appearance.