1. The built-in types are already protos. Imo gRPC wouldn't be a good fit - actually will make the system harder to use.
2. Already can be achieved today via kine[0]
3. Couldn't you build this today via regular CNI? Cilium NetworkPolicies and others basically do this already
4,5 probably don't require 2.0 - can be easily added within existing API via KEP (cri-o already does userns configuration based on annotations)
Apart from 1 and 3, probably everything else can be added today if the people in charge have the will to do that, and that's assuming that I am right and these points are actually that important to be standardized. However the big enterprise-tier money in Kubernetes is made from dumbing down the official k8s interfaces especially those related to access control (e.g. k8s own NetworkPolicy compared to Istio's access control related resources).
4,5 probably don't require 2.0 - can be easily added within existing API via KEP (cri-o already does userns configuration based on annotations)
[0] - https://github.com/k3s-io/kine