One of the main challenges has been making the map simulation work for hundreds of simultaneous players without the server becoming a bottleneck.
Most interactions are event-driven and the map state updates incrementally, which keeps things manageable even when many borders are shifting at once.
I've successfully tested this with 4096^2 maps and 1024 players and in those tests framerates were stable at 144 FPS, with the server ticking steadily at the standard 10 TPS.
It is built on Rust and Bevy. I'm happy to answer any questions.
How did you test with 1024 players - were they real? Often synthetic loads are very different to those caused by real players.