7. Squad Control
It may not seem an obvious choice for a game like Halo - where the protagonist often plays a 'lone-wolf' type character - however the idea is not completely far-fetched. In 'Halo: Reach', when you were joined by friendly AI, a marker would appear over the head of up to four 'marines' who would then follow you around - when possible - as part of your 'squad'. However, other than said 'marker' appearing and the 'following' mechanic, the squad feature boasted little else. With the protagonist playing the 'Master Chief', your character certainly has a high degree of authority over his fellow marines and some simple squad-control mechanics could add yet another dynamic to the gameplay. The mechanic would not need to be overly complicated, simple orders could include telling marines where to move, getting them to stay close, spread out, be aggressive or use cover and so on. It would not make the game 'squad-based', but as with Halo: Reach, if the player came into contact with up to four allies, they would have the option to use them to their advantage. This could provide tactical elements in open gunfights where the player is forced to face numerous aliens, perhaps having to defend or assault a certain position. If the 'Firefight' mode were to return, a squad feature with AI allies could make solo experiences all the more enjoyable.