https://news.ycombinator.com/item?id=49928566
Show HN: Giving Opus 5.5 a simulated paint canvas
It's well possible already, it's just inefficient.
Also of course you can (and always could) negative-prompt "artist signature". Or have the LLM give it a checkup with edit tools. This is all just a massive skill issue on the part of the people who set up the tooling.