This one is not listed on any official roadmap. I plan to discuss it with the community, and if there is positive response, to start driving this effort forward.
Kubernetes is implemented using Go. Go is a great language that puts a lot of emphasis on simplicity. As such, one of its prominent features is the single executable binary. There is no separate runtime, and until Go 1.8 there were no dynamically loaded libraries. That approach is great in many situations. However, it is a hindrance for flexible and dynamically configured applications. Kubernetes is, of course, all about flexibility and plugins. But those plugins (with the exceptions of CNI plugins) must all be compiled into the Kubelet or the API server. CNI plugins are a different story and are deployed as separate executables, but that limits the interface for standard input and output. That works for CNI plugins because the API surface area is limited, but is not a good option for many more interactive plugins...