As far as the limits of mobile computation goes, I think the thing to consider is that Qualcomm is already providing Wi-Fi 6E chips that have VR-class latency (<3ms) - this is bog standard, but of there are of course companies like Amimon that have been offering proprietary ultra-low latency (<1ms) solutions for a while now. We'll see if the PS5/PSVR2 offers a wireless solution, but I don't think it's too much to ask for those looking for cutting edge experience to use untethered, local compute - why do you need to strap an RTX 3080 to your face? There's already more than enough power on mobile to provide the basic I/O for presence and engagement in VR.
While I'm less sure on foveated rendering (although I'm really impressed by DeepFovea https://research.fb.com/publications/deepfovea-neural-recons... I wonder what kind of rendering pipeline will be required), I think basic eye tracking will be coming w/ Quest 3 as well - it's not only needed for DeepFocus, but also their Codec Avatars.
The stuff that FB has been showing off the past few years is insanely impressive - I think their mixed reality approach beats the pants out of what MS has been doing. I'm really curious to see what Apple has been whittling away at in secret - I'm doubtful if it can compete, but who knows? Google seems a bit out to lunch on all this.
My impression of pessimism came from his skepticism that Moore's law would continue long enough to get them to where they really wanted to be on mobile VR, his struggles with latency probably making cloud rendering a poor experience for most, recognition that they were already at the ceiling of their heat and power budget, his belief that foveated rendering was not going to save the day, his recognition that the lenses were now a limiting factor vs the screen for image quality and that other lens designs would be fragile and suboptimal in a shipping product.
I didn't mean to say that I thought he was pessimistic about VR overall, just that he didn't seem to think there were any large gains in hardware quality coming soon and it was down to the software to make full use of what was there.