So far, I don’t see anything that made the last 4.16 update release or any new commits to the 4.16 git branch that eliminates the need for patching SteamVRRender.cpp in order to get fullscreen mirror mode on the Vive.
As of today ( 6/8/17 ) when using the SteamVRRenderer, they are still clamping the incoming vr.MirrorMode 0-2, (the clamp goes away in 4.17, see Promoted branch ) so if there is a way to enable full-screen mirror mode it doesn’t look like it’ll be done the usual way.
Not sure about Oculus, I took a quick look, they do seem to support several more mirror modes, but we develop primarily on the Vive, so I haven’t needed to dig into it or test.
That little patch has become basically mandatory for our installed engine builds, customer facing demo’s, etc.