I'd really like to see genuine co-op play, where each player has a specific task to do in order to progress, or their own route to make sure the whole team can take down the boss. The closest thing at the moment is the Atheon fight with one team on relic and one outside. Even something as basic as having a section where one player has weapons disabled while they activate a series of confluxes/whatevers and the other two provide cover from higher up would be a nice change. If you think how much more replayable strikes would be if you had three different routes to choose from each time it could really add a lot of content. It shouldnt really matter that its only 3 either. When you think about it, the only reason you need 6 for the raid is for firepower (except atheon, and even then you could probably get away with a team of 3.), its not like you cant progress without a full team and I'd much rather see them focus on cooperative strategy than just increasing the number of enemies.