There is a log of emphasis going on in Kube right now in making sure that there is lots of room for experimentation around container formats, tools, and architectures - while at the same time, trying to keep Docker working well at scale and introducing Rktnetes. There's also work being done around runc support and VMs (from the hyper guys). Ultimately containers are just processes (some of them kernels), images are just another archive format, and the glue is what makes them interesting.

Disclaimer - I work on Kubernetes