In theory it's possible to build a standing wave on the retina, but to do it with pixel precision with a vrd/fsd is beyond difficult compounded worse by form factor.
I disagree with the article that rendering black is necessary for wide consumer adoption of AR.
I disagree with it based on my interactions with naiive (not an epithet) consumers who are playing in AR. They are excited enough about HMD AR when shown that shadow casting and an AR version of "presence" isn't as much of a consideration whether they would adopt or not. It comes down to "does this provide value." Shadows create realism and people are flexible with realism.
That said, "casting shadows" would be a huge benefit and I think it will get there eventually but there isn't a roadmap to it yet.