The testing of the release has shown a few important flaws in both the implementation of Windows 7 and Windows 10. Unfortunately, this means the feature is far from being good enough to release in 8.3. Work continues on top of finding out why the flaws were found so late in the development.Rowen Gunn commented
So it's "planned" but never released?! It's been 2 years... it doesn't take that long to add in FLUX support. Please our eyes are begging you, add FLUX support!!!