This is stated in various places on this website.
From the FAQ, 500 players is:
our pre-alpha number, and is what we aim our game will support at the very least, really the number is dictated by what a server can handle and we will try to push it as high as possible.
The other titles in the line battle genre are hovering at around 150-200 players per server, admittedly with different engines (FSE are building their own engine).
But I will be in awe if BCoF can achieve this without significant lag, especially in high density line battles. I’m no expert in these things, but my understanding is you’ll need significant computing power to constantly send 499 instances of data to all other players on your server?
If achievable, and I hope it is, 500 players per server would bring a whole new level of immersion to line battle gaming.