Scenes and prefabs have been able to be saved in a text format for a while. That said, they were still effectively unable to be merged in all but the simplest o

Scenes and prefabs have been able to be saved in a text format for a while. That said, they were still effectively unable to be merged in all but the simplest of situations for reasons I don't fully understand. Hopefully this was improved in Unity 5. One of the buried release notes mentions a new merge tool for scenes and prefabs in the engine.