I read earlier that you suspect this is the case - I did not see that confirmed in any way yet, so sorry, I will wait before I afford much value to such number.
Is the sub-pixel arrangement of the Pimax confirmed yet ? I may have missed that. Is it pentile like e.g. the Rift ?
Well, you will likely have a rectangular picture being rendered, then its put through the distortion mixer resulting in another (rectangular piece of) the picture being created and sent to the 8K. So yes, I would not expect the software to be smart enough because I fear all the games assume rectangular output. Only making the rectangle smaller will be used when they employ the 170° option.
As this is based on a rumored 50% effectiveness, let's discuss it further when the facts are established.
I would assume the mere fact that they have more physical pixels on the 8K screen and it is not matched 1:1 by the incoming picture data, this can result in unfortunate upscaling results while on the 5K screen it will just be shown as it was received. Smetime I guess you could choose between one of two colours for a pixel to be upscaled, and only if you downscaled from the large enough sample size will you make the "right" decision when down-scaling to get a good result when upscaling again to such physical pixel output on the 8K. But I admit I am still struggling a bit to appreciate why the SS beyond say 1.5 or 2 still shows effect. Possibly due to the enourmous distortions of a wide FoV lens.
And when we compare the 8K to the StarVR, we of course have to be fair if the latter is priced at 2x or even worse the price point of the 8K - but this again is completely in the dark at this stage (as well as the ultimate retail price of the 8K)