I'm just explaining why it's written 'x' and pronounced [ʃ]. If it pleases people to knowingly mispronounce Nahuatl loan words, they can do so, but it seems rather silly given that [ʃ] is also in the phonemic inventory of English. What next? Are you going say 'fowks pass' for faux pas?
Where I disagree is the premise it's supposed to be mispronunciation to say/spell a word differently than where it came from, doubly so when we change the spellings/pronunciations of our own words!