Is there some expectation that ISO 20,000 using a very average zoom lens is going to produce high quality images? If so, I think it's a fully unrealistic expectation. I think the sample HI 2.0 images represent exactly what can typically be expected when even such an advanced sensor is pushed so hard. The image is soft, it's shot at an absurdly high ISO, the lens is average at best, and vignetting is noticeable.
I think there are very slight variations in sensors. I think the sensor in the D800 used to make these snapshots is working perfectly well. I'd like to see some well composed, interesting subjects shot with the same camera set somewhere south of ISO 6400 and using an optically better lens than the old 24-120 f/3.5-5.6. If those shots show purple haze I'd be worried, but I doubt they will.