What you're talking about exists, and it's called Relationship-based Access Control, or ReBAC. There are a few implementations, Zanzibar paper, etc. The issue is not capability system, it's governance. The operator needs to write policies, of course! They don't want to read, write policies, audit other people's policies.

Sorry to piggyback, but if this is of interest to you, feel free to reach out to me over to email (contact info in my profile). I'm one of the founders of the most popular ReBAC solution, SpiceDB, which secures quite a few AI products including big players like OpenAI. I'm always interested in hearing about more use cases or where folks are struggling the most.