A RTX 4090 is about twice the price of and 50%-ish faster than AMD's most expensive consumer card so I'm not sure anyone really expects it to ever surpass a 4090.
A 7900 XTX beating a RTX 4080 at inference is probably a more realistic goal though I'm not sure how they compare right now.
The 4080 is $1k for 16gb of VRAM, and the 7900 is $1k for 24gb of VRAM. Unless you're constantly hammering it with requests, the extra speed you may get with CUDA on a 4080 is basically irrelevant when you can run much better models at a reasonable speed.
A 7900 XTX beating a RTX 4080 at inference is probably a more realistic goal though I'm not sure how they compare right now.