This is a bigger problem than people realise.
Think about it, how many millions of articles are posted online produced by OpenAI's GPTs to date... Good luck clearing out the training data for GPT-5.
True human content will get gradually scarce. We steer it for sure for our posts, but it is still GPTs that do the heavy lifting.
OpenAI's own classifier fails to detect GPT-4 generated text at the moment.