Returning to your original question about OAI developing specialized models, i had the same thoughts more than a year ago, and of course is a better (natural) option to have or trying to achieve it as per the benefits you described; but i’m not sure that from a cost/benefit perspective ($$$) of the LLM model creator would be so good idea.
Anyhow, today i guess its much better that someone like OpenAI offers a very powerful general model along with tools for the users, companies, groups, etc. who have the whole knowledge of their specific domain to adapt/customize/tunning the model for their needs.
Features like the system prompt and better if combined with RAG and the flexibility of managing via SDK can help you get a powerful specialized bot/assistant/agent.
(i may be wrong on this: i read somewhere that GPT-4 could have a MoE architecture and that the system prompt help in the “activation of the adequate experts”. - sorry if this wrong)