One of the defining features of Halo 2 was the ability to create a clan. Ranked clan matches were hype and having a pool of 100 players not even on your friends list made finding custom games incredibly easy. There was huge backlash from the community after it was removed from Halo 3.
PLEASE, 343. I implore you to add this feature to Halo 5. It is not present in any of the current FPS console shooters and it would set Halo 5 apart from the competition.