The engine is multi threaded, so no single thread problems here.
Furthermore in BCOF the network engine is a new Unique engine, that we specially wrote. It cannot be compared to the Mount & Blade engine's networking.
In theory we could do huge player numbers far over 500 players per server... As such we will surely keep our promise to deliver you the 500 players per server.
We will probably go (far) over it, but that's for later.