I'm wondering how much of the "DLSS 3 doesn't run on older cards" isn't about the OFA, but about how poorly DLSS 3 operates at low frame rates. Frame interpolation has three major flaws when working on, say, 30 fps input data, two of which Alex demonstrates pretty clearly here, and one of which he (understandably) skips.
First, the generated frames are worse. If you're using DLSS 3 to reach 60 fps, you're talking about 33 ms between perfect frames. That's a lot of visual change, and will be more prone to egregious artifacting.
Second, the artifacts persist longer to the eye. AI frames are 50% of the output no matter what, but in lower frame rates, the specific artifact is displayed for twice as long.
Third, and the thing that Alex didn't touch on, is that the latency impact is higher. If you're running at a native frame rate of 30fps, then you're buffering 33ms in advance of what's displayed.
I get that folks want the big cool tech on their next console, but even if someone can coax DLSS 3 to run on Ampere cards (and it seems like they can, but with frame stutters aplenty), it's probably not a fit for the use case folks want it for on Switch.