Alongside these amazing ideas, from a no life point of view. (That would be me.) I think Halo 5 needs more "incentives" to play longer.
Halo : Reach has commendations (Reason I still play it.) Halo 4's Commendations were laughable, and the rank is laughable. CSR? Sure, it's harder, but where's the reward for getting 50's?
So H5 just needs some incentives like the Haunted Helmet from Reach or getting 50's in every playlist like H3 for Recon.
I really think a mixture of Armor (for reaching Max Rank) and EXTREMELY cool armor effect or helmet, nameplate, skins etc for getting 50's in playlists AND something for reaching 100% commendation progress.
I would be on that like a fat kid loves cake.