If I stay at 3440x1440 then yes, even if a game in 3-4 years time comes out with twice the graphical demand of Cyberpunk 2077, then I can simply go from DLSS Quality to DLSS Performance as that takes me to over my framecap of 139fps (Gsync) whereas currently it sits at 120fps. I've already accounted for these variables of future usage of the 4090 in newer games that use path tracing. The chances of a future game being twice as demanding as Cyberpunk though are extremely low, We've already reached the peak of path tracing anyway and the rest is just technology maturity and developers getting comfortable with toolsets so I actually see things improving over the year not getting more demanding.
Even if I go 5120x2160 in a future monitor upgrade then the answer still is a yes. I'v only used 4k ultrawide so far using DLDSR and that has a performance overhead to factor in since the driver is doing additional processing and even that ran reasonably well at 100fps path traced, so a native 4K without the DSR overhead would be above that so should still be good factoring in the maturity benefits of future path tracing. Non path traced games will remain a walk in the park as they currently are even without frame gen on a 4090.
If I wanted 240Hz leveraged assuming I go for a 240Hz or greater display and I was dead set on "needing" to reach that framerate/cap then a 5090 may be needed, but I don't see that ever happening because I'm not one of those people who must reach that sort of refresh rate and fps max, past 120fps it's diminishing returns anyway and I prefer my 175Hz OLED running at 144Hz due to the native 10-bit mode anyway so it will remain like that.
Couple that with the advances in DLSS each update, DLSS Performance now looks almost as good temporally as Quality, for example, along with ReSTIR GI for Ray reconstruction that makes things more efficient and higher quality at the same time. All of this stuff is being baked into Unreal Engine 5 too as both nvidia and CDPR are helping that along due to the 15 year contract on using UE5 only by CDPR. We;re going to see some big gains in UE5 in coming years thanks to this.
I think people often forget just how far and away Nvidia made the 4090 in terms of raw power compared to everything else, it's been untouchable since launch 2 years ago, and will remain top tier for years to come really. No other card in all history has had that large of a performance delta from its lower model siblings.
Another one to bookmark. Thanks mate