Most games that do non-authoritative peer-to-peer multiplayer ultimately do something similar for singleplayer. Although it may not be as far down the layers as

Most games that do non-authoritative peer-to-peer multiplayer ultimately do something similar for singleplayer. Although it may not be as far down the layers as a local socket. Also, Minecraft uses something vaguely similar, with a separate client and server, with the client and server communicating locally via shared memory (effectively a local socket, but not bothering to bounce through the OS). Though Minecraft's an odd case - they used to not do it this way, and switched to it, and in the process broke a lot of things.