Is that a real boundary? I mean if an application asks the kernel to enforce a rule, the kernel enforces that rule, regardless of whether it counts as business logic or not. Why have two languages for defining such things if they're not actually distinct?

I'll admit that OS interfaces could stand to improve in their ability to do so, there's a lot of stuff in plan9 and fuchsia that I'd love to see in widespread use, but despite that I still think the quickest route to sanity is improving existing tools that constrain arbitrary processes, not replacing them with tools that specifically constrain agents.