I'm not so sure they would be able to easily update RSR to use FSR 2.0, since the new algorithm apparently requires more data than just the completed image. FSR 2.0 appears to require access to the depth buffer, containing the distance to each pixel, as well as a motion buffer, containing the motion of each pixel, to be able to predict where pixels rendered in one frame will appear in subsequent frames, making it more like DLSS. And I don't get the impression that a driver-level upscaler would be able to accurately determine how to properly utilize that data without developer intervention.
Of course there's also the consoles running AMD GPUs, which will likely make heavy use of FSR. And really, if you consider that there are close to 170 million PS4 and Xbox One consoles that many developers are still supporting, and already over 30 million PS5 and Series X/S consoles out there, along with around 20 million AMD GPUs being used on Steam, it's probably not accurate to say that AMD is a "minority provider of graphics hardware", at least in the combined PC/console gaming space.
Judging by Steam's reported monthly users and percentage of those with Nvidia hardware, we can extrapolate that there's likely close to 100 million Nvidia GPUs being used for gaming on Steam. Though only around 30 million of those are RTX 20/30 cards that can utilize DLSS. So there's somewhere around 200 million AMD GPUs being used for gaming, and probably a roughly similar amount of Nvidia GPUs once we add the Nintendo Switch, but fewer than 10% of those devices can currently utilize DLSS, whereas a majority of the hardware should be able to utilize FSR. And that's before getting into Intel's GPUs and the many mobile devices that should also be compatible with FSR.