The most useless thing is that to accompany a high refresh rate of about +/-150 on newest games on UW resolution 3440x1440 a 4090 is only about able to do that, and with appearance of 5090 surely you could gain a little bit more on that, but that resolution is lower in amount of total pixels compared to 4k.
So now 5k x 2160p is even higher amount of pixels over standard 4k, does anyone even understand that no card is able to run games on such screen on high refresh rate, unless youre fine with suboptimal feeling of 50 fps which then invalidates all the technology, features, and the refresh of such screens.
With this said, I can comfortably say that probably not even a 6090 will be able to do that. But it's definitely not a 5090. If you want an UW stick to 1440p uw.