Having ported a TeX distribution to MacOS classic some 15 years ago, I feel that the author overstates some of the difficulties. In particular, it's not all that hard to get kpathsea to work without callouts to bash scripts (it's not like Mac OS classic supported system() or anything like it). Basically, kpathsea is an API, and the implementation can be switched out (e.g. I implemented a dbm based file name cache).
Admittedly, getting everything linked into a single binary might be fairly hard.