Having a more community oriented game is a great way to keep players active and coming back. Halo 5 needs to keep players from drifting off towards other big games as casual halo fans may leave the game prematurely compared to more hardcore fans of the series (not talking about casual/competitive, rather big fans vs new players/ basic fans or players)
Having a more interactive community is a great way to keep casual fans interested while keeping more hardcore fans happy. Here are some of my ideas for more community interaction.
Bundling
A great feature for map makers would be being able to bundle a map and a game type together. This way, players can easily download a map and the game type compatible with the map. The map could then be selected in the custom games menu and the game mode would load up with it. From this point you could change or edit the game type if desired.
Voting
Allowing the community to vote on popular Bundles(above) for specific playlists would be great. When loading up halo 5, players would see a prompt asking them if they would like to vote, if declined the player can load up the community page in the menu to vote at any time the voting window is open (weekend voting periods, to be updated the next weekend). The voted bundles would need to be compatible with the playlist it was voted for, so infection can’t be voted on for action sack.
Community page
A page where many community stats are located, they would be broken into divisions. Divisions would be Most popular of all time, weekly, today and 343 favorites. These divisions would include maps, game modes, images, and clips. Bundle voting for specific playlists would also be available here (above).
Competitive
Global leader boards,friend leader boards, competitive history, player ranks, stat tracking(commendations) would be available on this page.
Event playlists
Once in a while events could be available, ranging from competitive to casual. Said events would have chances for items to drop based on performance in game. Drops would range from armor, nameplates and armor effects. So completing a Halloween infection event would give you a small chance for a jak-o-lantern EVA helmet variant for example.
Just some ideas 
feel free to add your own.