1) Cortana becomes overpowered by the didact like the prometheans did and is in a constant battle to keep control of her already rampant self. ( maybe turning from blue to a few pixels that are reddish orange.
2) somewhere around the end chief should retrieve her in a difficult boss fight against the new improved, stronger didact.
2a) during this boss battle cortana should be controlling promtheans and throwing everything at chief while hes trying to convince her to stop
3) forerunners
3) arbiter returns
4) more forerunner history is tied into the campaign
5) friendly prometheans
6) promethean vehicles
7) more tense action packed parts that make you constantly die.
Bring back a new , improved, harder to defeat scarab
9) involve some of master chiefs past
10) go to arbiters homeworld
