I thought one of the reasons Knuth made TeX was because there were no good math typesetters available. I have no idea if this assumption is correct, but one of the main reasons I've resorted to using LaTeX in the past is for the math typesetting. I haven't found any good alternatives, and it seems incredibly complex compared to basic kerning + line breaks and/or justification for regular English-like text layout.
So if this implementation lacks math typesetting, and that was one of the motivating factors behind the original TeX implementations, then I think this code is missing a pretty complex core feature.
Math typesetting was a goal, but it wasn’t really the main goal.
Knuth started TeX because the proofs for TAOCP Volume II were done with early phototypesetting equipment, and the results were terrible. Not just terrible for math, but very poor even for just regular prose. The reduction in quality from the Linotype machines used for Volume I was unacceptable to him, but it would have been far too expensive to revive that obsolete typesetting process for one book, so he decided to write TeX instead. His goal here was to knock the whole typesetting process so far out of the park that he wouldn’t have to deal with this same problem again for Volume III, Volume IVa, Volume IVb, Volume Va, etc, etc.
From the authors original post, it looks like you're right in saying that was not one of his goals.
This article says:
> Thus we can reasonably say that the code does contain an implementation of a very limited and basic form of LaTeX.
Which is what I'm primarily debating. I feel like a basic LaTeX implementation would at least attempt mathematical typesetting, but that could be debated :)
So if this implementation lacks math typesetting, and that was one of the motivating factors behind the original TeX implementations, then I think this code is missing a pretty complex core feature.