The "idea" of how NMS multiplayer would work is that the master server would get information of players entering/leaving a system, including when logging offline or off the game.
When the master server, possibly the same server that receives naming information of stuff, sees that two people are in the same system, it would then spawn a lobby server instance for that system to relay network information between players, sync up the orbits of everything so they all have the same time of "day" everywhere, etc.
This would generally just mean 2 people in the same server together. There is absolutely no reason, assuming it actually worked this way which it seems 100% certain it doesn't, that they wouldn't be able to pause and pause the other persons game where they could then unpause.
(This is also the reason why it's very clear it's not "server issues" and lots of people playing preventing this to happen. Even with a million people playing at the same time, simply receiving what star system players are in to coordinate when to spawn an actual game server process is super simple. This is very small amounts of data, like a timestamp, playerid, and systemid every few minutes or every few HOURS from the various players, so an average of a packet every few seconds)
Lots of games do similar things to this, so I don't understand why people keep insisting that being able to pause means no multiplayer. There probably isn't, but not because of that.