Well, the good news is, soon enough, you should all be able to make up your own opinion!
Very first screenshot of VR Fixed Foveated Rendering working in Flight Simulator 2020 with the OpenXR Toolkit
This is super WIP (Work In Progress) but very promising. If you take a closer look at the screenshot, you’ll be able to see the image going half resolution, then one quarter resolution, the further we go from the center of the screen! On this particular scene, the gain with FFR on was +8FPS (but with some noticeable degradation), and with some less aggressive foveation settings (almost no noticeable degradation), about +6FPS.
PS: I just got this working 10 minutes ago. So NO, IT’S NOT RELEASED YET, and it will not be for a little while.