Here's how a team of five programmers at Bossa Studios created Worlds Adrift, a sandbox MMO set in a world of a scale, complexity and level of detail never attempted before, where thousands of players can interact simultaneously, with no more effort than it takes to build a single-player game.
http://improbable.io/2016/02/18/how-a-team-of-five-created-a-next-gen-mmo-with-unity3d-and-spatialos
This post also goes into some detail, for the first time, about the Entity-Component-Worker model, and how it enables small teams to build games of such a scale and complexity in a simple and efficient way.
SpatialOS is available to Unity developers right now -- we can’t wait to see what new kind of games become possible when scale and complexity are not an issue. 10,000 players in a single massive FPS battle? Incredibly realistic worlds on your mobile phone? The kind of immersive experiences VR deserves? Up to you!