My guess is that the most obvious genetically rooted physical difference between humans today and humans 400 years hence will be their relative racial homogeneity. 12 or so generations in the modern world gives plenty of time for human beings to mix themselves up pretty well. Of course, there's no telling what effect futuristic genetic technologies could have. Maybe weird fads will catch on and people will want their kids to have prehensile tails or something. Assuming that the technology works, that doesn't strike me as a bad thing. I could use a prehensile tail, though I might need to buy new pants.
The Peter McAllister character cited in the article seems more like some dude who got a contract to write a provocative book (about how humans today are way less physically capable than those of millennia past) than any kind of expert. Google doesn't give me any sign that he has a Ph.D or an academic post or anything. Considering the impact of unsteady nutrition, parasites, and other problems of the premodern world, I'd be surprised if they were able to keep up with us.