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What is missing is some evidence (by which I mean ANY shred of evidence, not necessarily a full-scale research; could be circumstantial) that coders whose native languages lack the concept of upper/lower case ACTUALLY struggle more with this aspect of programming.

For what it's worth, we've had quite a few languages that only used upper case. Off the top of my head, FORTRAN or COBOL, but I believe it was pretty much the standard up until a point. Was it beneficial? Was there a detectable drop in productivity among programmers of Japanese/Korean/... origin once this trend reverted, and case-sensitive languages took over?

The article offers some food for thought, but objectively it does a better job riding the wave of current intellectual climate (inadvertently, perhaps) than producing a convincing argument in favor of the hypothesis.