Enchants for a dungeon work on a similar principal actually. If the dungeon can have an enchant, which i think all do, then it's guaranteed to drop from one end chest, regardless of players. Or at least an enchanted equip.
The enchanted equipment/enchants are usually in the same itempool, which I mentioned earlier, which is only present in 1 of the endchests in every dungeon (so for a solo run it is always present, and with 8 people in only 1 of the 8 chests.)
Enchants for a dungeon work on a similar principal actually. If the dungeon can have an enchant, which i think all do, then it's guaranteed to drop from one end chest, regardless of players. Or at least an enchanted equip.
As for having it out with other people... Is this community going to do free for all for items? I mean in live, i wouldn't accept someone in my party if i need an item and supplied the pass, unless they agreed to let me get the item should it drop. It was a fairly common standard, if you supply the pass, first call on item reward. Unspoken rule is that you only get one item reward, and the gold and not several good items in one run, but i never really had much issue with it. The few times someone did nab the item and wouldn't give it up, you can bet they were shamed and several individuals wouldn't trust them in runs again.
Anyway, it's all kind of a questionable point on this server, since you just buy the unrestricted pass anyway.
I'm assuming this discussion is about promoting people to party with people outside of their usual group. Of course, you can promise to give up a certain item if someone els needs it. When I was looking for my delusional cap, I'd just invite Uzuu or Aldoros to come with me since they would give it to me. And of course, even with other people, some might be willing to give up the item for you when they run with you.
But, the problem is that there is much less incentive to run certain dungeons if someone else wants to claim a certain item already. For example, I'd be totally cool with running with random people alby adv 3 for wooden needle if the system I mentioned was implemented where everyone has a chance to get a good item from the end chest. But, as it is currently, I won't invite random people, and just invite people I know will help me get the wooden needle since doing it with random people that also want it is just much slower, since only 1 chest will have a chance for it anyway.
And that unspoken rule you talk about, you mean like you aren't allowed to get a stamp item from the black golem in ciar adv AND get spike from the end chest? It is kinda finnicky what to count as ''several good items'', I personally have never seen it happen that multiple good items were produced by the same dungeon/SM (as in, a monster dropped something very good and end chest gave something very good.)