From what I can tell from this text, their solution to increase diversity is to add more dimensions on which to judge a candidate, since an infinite dimensional orange is all skin. In this way any given candidate could be judged as best so when hiring based on objective factors you can also give preference to diverse candidates.
Which seems to be a version of just arbitrarily choosing a candidate that you wanted to hire(for diversity purposes), but who wouldn't normally meet the criteria.
It's a pure political text designed to aggrandize the author without actually committing to a solution or another. He rejects affirmative action but then talks about multidimensionality as a tool to justify it in practice, as you point out.
He observes (correctly) that poverty is one of the strongest drivers of exclusion, which is a nice political trope, but then ignores that idea going further with his model of talent distributed randomly to spherical cows.
Well, guess what, talent is not distributed randomly, the way people get exceptional in one of their dimensions is by practicing and developing it. When a series of great filters are applied beginning in kindergarten for some people based on some factor of race, class, gender etc., they will not have ever had the chance to develop relevant aptitudes and will always look flat no matter what projection you apply to their sphere.
My reading of the text is that "dimensions" he is talking about are the various ways of being good at physics, not the many ways an individual person can be talented. From the text:
"...What this suggests to me is that there are a huge number of ways of being a great physicist and that in turn suggests there are many ways of being a great physicist that we haven’t seen yet. Diversity is critical to the future of physics, I believe, because it is imperative to explore this vast space of physics talent and that means encouraging people who are different and who think and act differently..."
Which seems to be a version of just arbitrarily choosing a candidate that you wanted to hire(for diversity purposes), but who wouldn't normally meet the criteria.