I don't disagree that it would be a nightmare, I've just be thinking in my head how it could be done.
Server: Events to poll the server game, update the database, poll the database for client changes, update server game accordingly. |Client;
Client: Client plays the game, client 3rd party software uploads player's changes to the server database, polls the database for changes, downloads the changes, updates the clients game accordingly. |Client|Server;
I think a system like this would be quite speedy. Something like UO circa 1999.
I know there's a lot more under the the hood of the game that doesn't help MP like script systems that weren't developed with it in mind; I'm just speculating a logic.
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