Multiplayer - use autosave file if possible instead of sending a new save every time

[obuw]

This is probably my biggest annoyance in multiplayer right now. The longer we play the larger the save file gets. Right now the 20mb save file takes ~5 minutes to transfer with our garbage 3rd world internet upload rate. Every time one of us dies we load the last autosave, and the one who joins has to wait 5+ minutes.

Wouldn't it be so much better if the host and each client autosave at the same time, and then when a new client joins a server, if they have the same autosave file the game was created in (and the game was created less than a minute ago), the host just skips the whole sending process and only the "catching up" part has to be carried out. This would reduce join times from 5+ minutes to mere seconds and I think it would be a huge QoL improvement.

As a further step, the system could even be made dynamic, so the client calculates how long the "catching up" would take, and how long receiving a new save file would take (with a quick download speed test), then it would automatically decide whether it would for example be faster to get a 20mb save file, or do a "catching up" process of the last 20 minutes (the time difference between the host and your autosave file).