VRSS is different than VRS: 
This is only working for forward renders and FS2020 is most likely a deferred rendered instead.
Here is the relevant information:
VRWorks - Variable Rate Shading (VRS) | NVIDIA Developer
But it appears this one also requires a forward renderer only…
Nevertheless, the same principle could be implemented in the FS2020 rendering engine shader code in-house instead of using the Nvidia VRWorks library, in applying the same idea: where things are moving don’t pixel shader finely. By the way the FS2020 rendering engine is heavily using this kind of technique but spreading computation in time instead (clouds, reflections, shadows are computed over multiple frames).
In turn, although VRSS and VRS NVidia technologies are requiring a forward renderer and couldn’t be applied as-is in FS2020, their operating principles could be somewhat implemented in-house to some extent. I believe it is not much critical at this point because the rendering engine (at least the pixel shader part of it) seems already quite well doing.
However the DLSS2.1 technology (with VR support) is evidently a much more important tech to consider right now than any other in my opinion, because it shall have dramatic and immediate impact on the perfs, especially in VR. It won’t solve the other rendering engine problems (and I believe there is a huge one introduced with WU3 and the VRAM buffer management) but it will help in any case today, and once the rest is also optimized it will give additional boost nonetheless.