In a VR-enabled scene with the Oculus Rift connected and VRSettings.enabled false, you can make VRSettings.enabled become true simply by clicking in another application (such as your web browser) then clicking back in the Unity Editor. Changing application input focus like this should have to effect on VRSettings.enabled.

I set the Severity high because this is one of the use cases defined by Unity VR devs (test G.2) in the Oculus Integration Verification Tests.