Operating Systems exist to manage access to resources - which requires a very different sort of training than user interface AI's.

Computer chips already use ai/machine learning to guess what the next instructions are going to be. You could have the kernel do similar guessing.

But I don't think those AI's would be the same ones that write love letters.

I think what we'll see is LLM's for people facing things, and more primitive machine learning for resource management (we already have it).

Sorry, I'm partially responding you and partially to this thread in general.