While the support itself doesn’t necessarily mean OS-level toggle like the Steam Deck has right (which I believe is still at FSR 1), it still could be a nice touch for the titles that choose to implement FSR 4.
Maybe the community adds the OS-level support unofficially, somewhat similarly to Lossless Scaling right now (although perhaps for free). This is just my uneducated guesswork, please see this comment for proper expectations:
“Supporting” and “working well” are different things though.
Without the low precision/specialized instructions of newer hardware, there’s just a fundamental limit to what can be done without the overhead of FSR being too much. Though there are certainly some implementations that could work on older hardware, I’m sure.