Falling under the category of 'harebrained schemes' is a project that combined NVIDIA's frame generation (DLSS 3) with Team Red's own take on this tech, AMD Fluid Motion Frames (AFMF).
Surprisingly, it is possible to stack up and use both these rival technologies together, and doing so can boost frame rates massively - up to tripling them, in fact - but the full story is a lot more than just frames per second.
QuasarZone (a Korean tech site) carried out this experiment (flagged up by VideoCardz), using a PC with two graphics cards inside, one NVIDIA and one AMD as you'd expect.
Essentially the setup has the game rendered by the NVIDIA GPU (an RTX 4090 in this case) with DLSS 3, and then the AMD graphics card (an RX 6600) applies AFMF on top of NVIDIA's frame generation, before outputting to the monitor.
In other words, this is two passes of frame generation, and as mentioned it does indeed work and boosts average frame rates hugely. Cyberpunk 2077 benefited from a massive 290% boost in average FPS, going from 71 FPS native (4K ultra, no ray tracing, no upscaling) with the RTX 4090, to 209 FPS with both takes on frame generation applied. (With DLSS 3 alone, the test rig hit 105 FPS, so applying both made a big difference).
Of course, average frame rate is far from the full story of how smoothly a game runs and feels.
The trouble with this fudged twin GPU setup is that it can have very unwanted side effects, increasing average FPS but also causing more drops in frame rate (worsening of 1% lows) in some cases.
Given that, it's likely that the overall feel of the game will be jerkier, and also with such a setup, you're going to experience a deterioration in image quality and you're likely to run into visual glitches and other problems.
Remember the heady days of SLI (or CrossFire) configurations and how that never worked out quite how it should? If even an official dual graphics card solution like that ran into trouble with some games, imagine how patchy this experiment will be in places. (And yes, SLI does still exist, sort of, but not for gaming in any practical sense).
Back to this experiment, and to sum up: yes, you'll get big frame rate increases, but no, it definitely isn't worth the trade-offs (which include the extra power cost of running two GPUs, of course), or the hassle of getting it all working no doubt.
If you want the smoothest frame rates possible, then simply buy an RTX 4090 - though the pricing on the Lovelace flagship is sadly going through the roof right now.