When players defeat an enemy in co-op, loot is instanced. Basically, it’s not shared, and each player gets their own.
We also learn that you actually need four players to do the Stronghold endgame activity. You can’t go solo or with an incomplete squad. That being said, there is matchmaking, so finding people to go with shouldn’t be an issue.
Strongholds are not part of the campaign, but they’re high-difficulty endgame experiences. Story missions can be played solo. They’re easier with a group of four, but they adjust automatically depending on group size. Missions are “relatively linear.” On the other hand, free play is “wide open.”
When you complete a mission with a group, you remain linked even after you go back to your base. This means that if you want to go do something else with the same people afterward, you can do so without having to redo the party.
Players will be able to create different freelancers on the same account, so you won’t be limited to a single persona if you’d like to have alts.
Last, but not least, Gear can be used across multiple loadouts so you won’t need multiple copies if you want to use the same piece of gear across different equipment sets. Gear is specific to each kind of Javelin.