The world of publishing is certainly seeing the attempts for such an llm:

https://www.npr.org/2023/02/24/1159286436/ai-chatbot-chatgpt...

And I do wonder how difficult it is now. We have datasets like libgen and Anna’s Archive … are there public llm’s out there that have been trained in this way?

Probably the next best thing: I think Microsoft Azure still offers access to the GPT-3.5 base model (aka code-davinci-002). But OpenAI removed it from the API. Too powerful perhaps.

> Too powerful perhaps

no, that's pure marketing. They have difficulty scaling it in a cost effective way. simple as that. Everything else is just sales talk

When the removed the base model, they didn't remove text-davinci-003, which essentially is the same GPT-3.5 model, just with fine-tuning. So your explanation doesn't fit.