Make it so we can choose their equipment from items in our vault or on other characters and it would be pretty awesome to form your own fireteam with your own characters I wouldn't have to worry about teammates suddenly deciding that he doesn't want to shoot anymore and just sitting down. Might have to make some pretty smart AI though.

Before everyone decides this would be good for Destiny, I just want to bring something to everyone's attention. Titanfall did this and it wasn't very good IMO and everyone else's opinion. Bots were stupid and they were pretty pointless throughout the game. Just a thought.

Having NPC allies instead of enemies could be interesting under any circumstances. Maybe you could finally give Cayde what he wants and take him along with you. Or, you could assist the Sunbreaker titans; like the Awoken they have no allegiance to the City but they and you might share a common goal. Or consider this: one of Destiny's most annoying aspects is that the Darkness and its minions (Vex, Taken, Hive) are intent on the destruction of humanity, but they are also an enemy to the Fallen and the Cabal. Despite being surrounded by a nearly all-powerful force that seeks our mutual annihilation, we still insist on shooting at each other. Maybe there could be missions where these races temporarily set aside their own disagreements in the face of a mutual threat. You could have Vandals or Captains fighting at your side, or a row of allied Phalanxes to hide behind while your shields recharge.

Halo always did decent mission where NPC's Destiny could do the same. Why is it that we never see New Monarcy or FWC troops fighting/ scouting on patrol? Or Dead Obit scouts looking for resourses.