OK, so there must be several factors at play, here.
First about the render order discrepancy on PC with or without Oculus, this shouldn't happen as far as I'm aware. We'd really appreciate if you could send us a minimalist repro project showcasing the issue.
Now about the "always on top additive meshes" issue on Android. This may be a bug in our GLES implementation, we'll investigate. If you could provide us with screenshots of the result and the expected result, that would help greatly.
The "HasPostFx" checkbox is actually a workaround for DirectX' texture mapping's origin being top-left instead of OpenGL's bottom-left (as documented here : http://wiki.popcornfx.com/index.php/PKFxRenderingPlugin_component#HasPostFx),
so it has no effect on Android.
We actually support the platforms/graphics API combinations described in the table I linked earlier.
VR-specific bugs encountered with Unity's native VR support are most likely on Unity's part and come from discrepancies in their implementations of said native VR support and the the aforementioned command buffers' native plugin interface.
Edit : Oh, and the plugin should be full-featured full-support from Unity 5.2 on. unfortunately we're not exempt from regressions due to Unity's changes and it might be worthwhile reporting those to them.