I think LLMs may have a role in security posture, specifically flagging/identifying potential threats for human review. But a Zero Trust/Access Controls should be a HARD boundary, not an inconsistent one.
The problem we have right now is that there are some legitimately interesting ideas out there for things we could be using LLMs for, but we also have a ton of "I have a hammer, and everything looks like a nail" going on too.
It's not a problem as much as a phase the world is going through. LLMs are a technological breakthrough in the same generality class as the Internet, or possibly electricity, and in both cases the world went through a phase of attempting to apply the newfound invention to literally everything. It's a necessary phase, when a technology obviously could be useful for everything, but it's not obvious whether it will in practice.
Sounds like adding the LLM in would be on top of the existing deterministic controls.
Existing controls handle the "Should you be able to access this resource right now?" the LLM handles "Is this user behaving as we expect them to while accessing this resource?"