There's a serious proposal along the same lines: https://www.unicode.org/L2/L2025/25241-ai-watermarks.pdf
(Flashbacks from the horrors in the Byte Order Mark wars)
Maybe considered serious by its proponents.
> For example, every other letter in this sentence is U+2060.
No it isn't! The PDF renderer has stripped them out.
I feel like there is an unofficial version of AGTI already in place for certain AI providers.
Whenever I generate a large amount of code, there is a ~20% chance that my editor will pop a warning "Some unicode characters in this file could not be saved in the current codepage".
I suggest taking a look at the raw outputs of a major AI provider in a hex editor. That (zero-width) whitespace could be hiding a lot of information.