At the moment most quests in it arent shared and you cant really contribute anything besides resources to others quests. Your quests are completely individual to you and its as if you are playing your own game but in same world as others where you can interact with them. I havent done any of the simultaneous freighter quests but they are meant to be incorporating more ways to share experiences.I haven't played a lot of No man's sky multiplayer but yeah I do remember joining a random player's game when i finished all the story, and the other player was just starting.
But correct me if I'm wrong the only quest that you can share simultaneously are the quest from the freighter terminal ?
I don't think multiplayer would throw the game of balance. As you said being a henchmen in another person's world would work great. And yeah I agree maybe have side missions that can be progressed simultaneously in coop across saves, without affecting the world or story.
Something that I think could be interesting also is what rockstar does with GTA V and the upcoming Red dead 2. If they made a separate multiplayer mode with its own map (copied from the single player) and own quests.
Although that probably would had an extra year to the games dev time
The thing they said about henchmen in previous games was that players didnt want to be relegated to a simple henchman and wanted to be their own hero. So they would have to find a way to make you feel important and like you are contributing or achieving something too.
Depends on budget and manpower, Rockstar have a huge budget and a very large team and multiplayer is still launching at a later date and proper multiplayer for No Mans Sky launched 2 years later than the game itself but they are a tiny indie studio.