> I want to try replacing all of that with a simple, unified API which lets you say "tell me the state of <kernel resource X> and tell me when it changes".

Fuchsia's "Signals" are designed in that direction. You get a "handle" to a resource, and the resource has a 32-bit integer with signal bits that you could subscribe to. The meaning of each bit is different for each type of resource.

(In general operating system terminology, "Signal" means just a message without any payload that would have required any memory allocation. There are many ways to do it, not just the Unix way. Message ports and other abstractions are sometimes built on top of types of signals)