> written using Indian abugidas and largely prisoner to a confluence of religious affectation, court ritual and the popular language of the peasantry as popular literacy never occurred

I agree that Thai is in a completely different language family than Chinese, but I don't see what this quoted bit has to do with anything. (And surely it would apply just as well to their neighbors to the west, who do speak a Sino-Tibetan language)

I wonder if that’s what led to original Assamese dying out.