It feels to me that this is a request for a feature which will be useful in some, but not all, communities.
I personally would be happy to see machine-generated text always hidden inside a spoiler-like mechanism: I want to know that this is what it is, and I want to know it before I invest time in reading it.
It would also be an opportunity to put something in the local rules: failing to delineate your machine-generated text is a flaggable offence.
Putting machine-generated text inside a spoiler-like mechanism also allows the poster to add some commentary or description: they might be including the text because it is amusingly wrong, or educationally wrong, or because it is useful.
The issue of future language models being trained partly on the outputs of older language models… that’s probably a big problem, bigger than spoiler tags.