Honestly, I wish rkt would get some more momentum. In my opinion it's superior to Docker.
OCI doesn't have an equivalent to discovery yet, but presumably it'll be something similar to the appc spec (https://github.com/appc/spec/blob/master/spec/discovery.md)
I also recently talked to some CoreOS devs at Dockercon and have started considering extending rkt to better support OCI runtimes (and images though images are "supported" at the moment). Exciting times.
I wish the market of container images had more competition. Right now there's Docker Hub/Quay (expensive, lots of features) and Amazon ECR/Google Container Registry (cheap, few features).