[palmotea]

> If they do, then AI writing will incorporate them.

Eventually, but at least for something like "ain't" the hill to climb to get there will probably be a lot higher, because you've got decades if not centuries of explicit discouragement and very little presence in existing formal writing (and maybe online writing period).

The more durable proof of humanity will probably be hyper rapid slang evolution, but that's going to have the downside of social fragmentation and making the past less legible. If slang changes rapidly over the course of a year, will anyone still remember the slang from 10 years ago to understand an old post?