I briefly worked on a game like this in space. It was a 4X game where the primary mechanic was the hard speed of light. Not only did it take years for your me

I briefly worked on a game like this in space. It was a 4X game where the primary mechanic was the hard speed of light. Not only did it take years for your message to reach a colony, your knowledge of the state of the colony was equally out of date. Part of the idea was that each player would never see the absolute coordinates of any star or another player’s names for anything, so it would be nearly impossible for two players, talking outside the game, to figure out if they were allies or enemies in game. What killed it was that players basically had to be able to send free form messages in game, to handle the complexity of negotiations this situation would require, but it would be far too easy and rewarding for two players to just share an email address, which would allow FTL communications and break the game. The only effective solution was a human GM filtering every message, which was awkward when the timing of message delivery was THE core mechanic.