(please see this image for reference: Imgur.com)
The basic idea of the Neighbours mod is to make The Long Dark a share-able experience without making it multiplayer. Players survive in singleplayer the same as ever. What the mod would add--as I propose it--is a "drop box" (also called a "cache") inside the game world which is synchronized between two players across the internet. This allows the players to trade items with each other across game worlds.
This concept models two wilderness survivors who survive in the same area, but never meet each other because the woods are too large, and because they don't trust each other enough to cooperate substantially. They're not friends, they're neighbors. They only trust each other enough to trade items with each other via the dropbox.
The way this mod could function should be simple: each game client already relies on a save file which can be edited. The mod concerns itself with one--or maybe a few--"container" entities that exist in the save file data, which correspond to containers in the game world at some central location or locations.
When player A adds or removes items from the dropbox, the game client should then automatically save to the save file. The mod client then synchronizes that save file with the game server. The game server then reads that save file and synchronizes **only the dropbox data** with corresponding data in player B's save file. Then, at some point, player B synchronizes their game file with the server, and when player B loads into their game world, the world is the same as they left it, except that new items now exist in their dropbox. (see attached image for a graph!)
Obviously the first challenge is to logically order and restrict the synchronization so that the clients avoid duplicating or deleting items. This is up to the developer.
---That's the basic idea for the mod. There are tons of variations that could be built upon it. Here are some other ideas I had:
1. More than 2 players. Maybe 4, or more. All 4 could share 1 dropbox, or there could be some large number of dropboxes so that pairs of players within the "neighborhood" could have 1 dropbox that's exclusive to each other.
2. A separately run matchmaking service. The original idea is obviously that you could share playing The Long Dark with a friend you already have, but randomly pairing two people on the internet together and encouraging them to cooperate to survive would create a very interesting model of the real-life scenario where two strangers are surviving in the same post-apocalypse wilderness.
An extreme version of this would be to add a sort-of "dating app" element to it. The matchmaking service could put two people together, but refuse to share any identifying information between the people, or to allow them to communicate with each other other than the most basic "Request X number of M item." Instead, the players would both have to survive past maybe 50-100 days before the server would present them with the opportunity to communicate. No, I'm trying to create a dating app. This would model the process of building trust between people, and it would also create an intensely emotional incentive to survive and to help keep the other person alive.
---Concerns: Cheating. Aside from avoiding synchronization exploits that would allow for duplication, it would probably be good to find a way to make sure that the players weren't simply editing their own save files in order to survive.
for discussion, this essay is also posted on reddit, here: Reddit.com
Interesting idea, I have to say that the way I would implement is simply to synchronize the box data, sending save files and parsing them server side would be too much unecessary overhead, but that's just semantics. How did you intend to match these players? If they're just randomly matched, there's the problem that you get matched with someone who doesn't use the box and then it's completely useless.
On the other hand, some kind of universal box, which holds the same items for everyone would be interesting idea too, but the main problem is that items can be added with save editors and other mods. But that could probably be solved. Now obviously the main reason I'm not too keen on implementing it, is that this will definitely need a server and that costs money.