I'm still interested in this line of enquiry.

These models are clearly not good enough for decision-making, but still might tell an interesting story.

Here's an easily testable exercise: get a load of news from somewhere like newsapi.ai, run it through an open model and there should be a clear discontinuity around ChatGPT launch.

We can assume false positives and false negatives, but with a fat wadge of data we should still be able to discern trends.

Certainly couldn't accuse a student of cheating with it, but maybe spot content farms.