Thanks to my Awesome Friend (you know who you are) for feeding me a piece of information today, that immediately made me feel extremely depressed and worthless. I am of course, an emotional windbag. That said, after taking a break and realising that emotions suck and logic and science must prevail, I update my knowledge on VRS.
I'll make it clear:
VRS isn't related to the precision of the calculations performed by the Stream Processors in the shader array of the GPU. It is performed by the Rasteriser, by allowing the 'Shading Rate' to be selectively reduced in certain parts of the sceen.
Shading Rate is similar to resolution, of the final image, in that a lower shading rate would appear more pixellated. The result is in some parts of the sceen, less shading / raster resources are needed where the image quality isn't largely affected; allowing for areas that would have a high impact on IQ to be shaded with full accuracy, quicker, increasing overall FPS.
My previous interpretation involved the precision at which shaders were run; for example 16 and 32-bit; the former being faster on hardware that can accelerate it.
I will update my current Hardware Profiles with this new information.
Ultimately: Vega (GCN5) and Navi (RDNA1) do not support VRS in the Rasteriser, but they do support using lower precision shaders at double speed.