BTW, I'm 99.9% sure I understand now perfectly what Pimax claims and how brainwarp works. This is what they said:
"Pimax 8K renders a single 4K image at 180 times per second, but users perceive a complete 8K at 180 Hz with high frame rate."
So it's actually quite simple indeed. In this particular case the game renders 2*4k at 90 hz. However Pimax claims that if they send the 2 eyes async at 180 Hz that the brain actually perceives it as 180 hz, just like @Headcool understood it too. That indeed MUST be Pimax idea of brainwarp, I'm 99.9% sure.
So IF this were true then a game could just render at 45 hz 2x4k. Then Pimax takes the left eye render, forwards it, then takes the right eye render and forwards it, so at 90 hz and then it would feel exactly like 90 Hz. However I'm pretty sure this is nonsense. No way the brain is going to feel it's looking at at 90 hz game when you forward 2 images that belong together, created at 45 hz, async, I don't buy that at all. There's just half of the game data missing. I even doubt sending 2 images that belong together async makes ANY difference at all to the brain. Maybe there's some slight effect, that the brain tricks into thinking the refresh rate is slightly higher than 45 hz but NO WAY it's going to look as good as 90 hz.
I think it would already look a bit better if the game would actually render (alternating) one eye at 90 hz, so each update the HMD actually would receive new game data (representing a new situation in the game). However again, in this case the game would need to support it and secondly, it's highly inefficient like @headcool outlined before. But I'm sure that in that case it would at least look better and closer to 90 hz.