There is a lot of evidence that language drives cognition and there have already been instances of ANIs creating their own efficient languages. Imagine that the year is 2040 and euclidian encryption is augmented via transcoding into AI languages to safeguard against quantum computing or replaced with quantum-resistant algorithms altogether. A turing complete quantum processor was actualized a few years ago, or we just finally figured out that ML and the probabilistic nature of Quantum Computing are a perfect fit. People tend to vastly underestimate the rate of progress over 10+ years.
2nd of all. I don't expect GPT to be able to reliably replicate the style of every person under the sun and neither should you. If you want a different tone, style etc describe the tone or style(flowery etc). Some people it can emulate very well, others it can't. That would be the case, human or not.
I can't help but think that social networks and search engines will start to negatively rank AI generated text. In my opinion, this would impact many more people than we think.