This is an easy idea that would help with purchases of the campaign. Why not offer a set amount of in game currency and special in game cosmetics with the purchase of full game? This would make a lot of people happy who play campaign and multiplayer. Might even get people to buy it just for the perks alone who play mainly multiplayer.
Also a cool drop in based firefight mode would be fun. Similar to the the survival concept of the old firefight but in order to get back in the fight you need to be dropped in by orbital drop pod. Either activated by team mate somehow or through a set amoint if lives. This could open up a fun concept for firefight and also custom battle royal modes through the drop in system.