you need to keep an eye on where tex spends its time on, and much is related to loading fonts, reading files, saving output, etc and with multiple threads one would have to coordinate that and make sure the time spent on it does not become larger overall

for instance, in your document making these large tables takes a while only because bTABLE is not that fast, so when at some point i can redo part of such mechanisms in lua we might gain way more runtime than by running distributed

Hans