You pretty much listed all the examples where that’s done (x-ing is also a big one, on signs), but there are way more cases where no one would ever use the letter X like that. I think parsing that kind of “syntax sugar” takes more cycles than a lot of people care to spare just to understand what a stranger is saying online. It’s too loose to be commonly applicable. Things like “Xmas” are accepted on a case by case basis.

The argument wasn’t made out of principle, either. If it were more widespread, it would be worth the potential confusion. It’s just not. I agree with that.