I agree tbh even Fhd(2k 1080p) looks great up converted. But the dsc is what PiMax was trying to get Nvidia & Amd to support (hard to believe ARM is ahead if them lol)
But as for can current gen cards push it? I would say yes as Pi Render X target resolution( I find 1.5 - 2.0). But then you may need Anti Aliasing to get Native 4k rendered. At present we render higher to get better quality image by Down sampling to 2.5k then interpolate to 4k. Which produces an amazing picture. Of which without doing an in depth comparisons. The mass majority will not see a real difference as it would require far too much concentration. Now a very small percentage will actually see the difference without being told there is.
As the old 1980's Laundry detergent said "I can't see the difference; can you?" -why pay more.
Movie/video wise? Unless its a 360/180 video; you will not have 4k like watching a 4k monitor. As Regular/3d video is often presented on a screen in an enviroment. & the 4k native is split between 2 eyes in a vr headset.
Per Eye resolution is "what you see"
Both eyes added together = Gpu muscle req to deliver per eye. (now 200°+ will be different as less binocular overlap)
But I agree atm 1) Ghosting 2) Gyro calibration/stability.
4k native? Wait til new DP standard comes out & stable(3-6 months after released) or wait for PiMax 4k Extreme v2.0 that will maybe support oled/DP/Usb3.x/Man Focus!ipd (say made for 20/20 with 1.5mm +/- in/out) USB3.x micro plugs for accesories
& maybe enthusiast friendly for future PiMax hrdware upgrades