That's might closer than you think I guess. The thing is that the new Assist pipeline is fully customisable and can use other models as well. They already have a ChatGPT integration which does not able to control entities in HA but at least you can have a conversation with ChatGPT in speach trough HA.

So if you spin up somehow an LLM model locally and connect create a HA Assist pipeline with it and than you use Willow(s future release which should be able to leverage the new Assist featre) as a phisical interface than you are golden.

It may be hard or impossible today but I think within months HA and Willow will mature into a state where tha bigges problem will be the training and runing a good enough LLM model locally. But I bet a good amount of hackers are already hard working on that part anyway.