The writer makes some interesting points, but ultimately his analysis fails because he neglects to address the main reason why anyone would use x32 instead of x86-64 in the first place - the reduction in size and cache impact of pointer heavy dynamically allocated data structures.
This makes a big difference on some applications, on the order of 40% on both Atom and Core i7, as demonstrated by non-trivial benchmarks run by the x32 ABI developers. Is that enough for a distribution to support x32? I don't know, but it is certainly not something to scoff at.
One worthwhile point he makes is that most x32 applications will run on an x86-64 kernel, so kernel performance will not be improved at all. I don't know how many embedded systems are kernel performance bound, but if it is important enough surely some way could be found to support an x32 native kernel as well.