There will always be this uncomfortable balance between need to know information to be useful being essentially the same as everything an adversary would need to really act against you.
With something like chat gpt being plugged into some voice assistant thing and having access to all your documents, emails, and other content, you could imagine having conversations about work content, content creation, calendar management, etc. Basically it would become like a secretary that is able to write letters based on your input, manage your calendar, etc. It could be pro-active and remind you about things, summarize incoming messages, search through your documents, message history, etc.
That's where AI becomes really useful. But the issue of trust is a big one. I don't think a lot of this requires a lot of breakthroughs either just a lot of integration work and engineering. Chat gpt is more a proof of concept than a well integrated thing at this point. It basically is running in isolation and it's only window to the world is chat. Changing that should not be that hard. Running things locally might help with this but it may not be a hard requirement for this. All depends on how useful this is.