Players would be able to play among other players in the same way that the existing multi-player modes allow them to - except there'd be no PvP.
Activities for wings and squads exist, as does multi-crew - none of them require PvP. Playing among other players can be rewarding in and of itself. Not everyone goes AFK to complete wing missions without actually playing the game - that some use them that way is not unexpected, however it's not the only way to play.
Wing trade vouchers, wing bounties and wing mission rewards all specifically reward multi-player.
It would offer the ability to play among other players in a PvP-free environment - which Solo does not do.
Offering the ability isn't going to do much good, because playing among other players offers no meaningful benefit in any gameplay other than PVP.
Squads already have private available for their group activities, and engaging in group activities within your squad and some other rando hanging around doesn't alter gameplay in a meaningful way. You may be able to recruit that rando, but his existence is a statistical improbability and shouldn't be counted on. You're better off stapling a flyer to a telephone pole outside your house for squad recruits.
Multicrew offers little to no useful gameplay. I'm gonna rant on multicrew for a moment: Srsly, how useless of a game mode can this be? You're gonna have your buddy fly the fighter? Why not just have him fly his own sidewinder? He's gonna bring just as much firepower.. Ooh, he can fire the turret, and do a worse job than the computer. Or, he can just sit there minding his one pip. Multicrew was waste of development time... The only people who benefit from it are multiboxers letting their alts sit idle in the passenger seat.
Wing trade vouchers are poorly realized. You need two players to be at the same station at the same time. If you're doing trading, then for this to be the case, you're gonna spend more time waiting on your fellow player than you are actually playing the game. So much of wings is sitting around waiting for the other guy to arrive, because space is so dang big and we need to stare at the void to make sure you realize how silly big space actually is. Wing bounties are great... it's awesome that further trivializing trivial content can offer a greater rewards. Wing missions... we went over this and I don't feel like I should need to repeat myself. Wing trade missions work in theory, the more players participating, the faster the mission completes, the less money spent on commodities, but, trade isn't really a group activity. You aren't playing together. You're separately working on a shared goal. Completing the mission solo is functionally identical to completing it as a group, save for the reward portion. Multiplayer gameplay needs to be judged by the actual gameplay, not the fact that you get better rewards for pretending to do it together. There is the uncommon soul who will play out a combat wing mission as intended, but most often they are cheesed by killing low effort pirates at the res. We can't measure the game by the rarities when there is a more common denominator.
For multiplayer to be meaningful, there would need to be a means to unite players who are interested in similar activities and are of similar skill level, otherwise you just have two people doing two different things in the same general area. Because the skill levels of players can vary so greatly, and there is no sorting mechanisms available, just meeting another pilot out there isn't going to be sufficient. The odds of players running into each other is slim as is. The odds of players looking for the same sort of gameplay is slimmer. And, the odds that their skill levels will be in a place where that gameplay is fun and engaging for everyone is slimmer still.
Yes, the things you've outlined might be true in a perfect world if the game were well implemented. But, we exist in this world, with this implementation. And, simply adding a "No PVP" flag would not offer any meaningful difference to gameplay, other than create whiners who are complaining they can't shoot other players, and creative griefers who find ways around those restrictions.
To promote good multiplayer PVE, the game would require significantly more thought than just this. And, based on how ad nauseum these discussions have gone and how little the people who actually develop the game care about what is posted here, it's not a conversation worth having, unless you enjoy the clicky clack of your own keyboard.