I think the Alpine Linux image for Docker is a good solution to the point about userland bloat. Much better than unikernels, which would entail giving up all the benefits of running containers on a shared, mature OS kernel, particularly with regard to performance, resource pooling, and debuggability. I'm still waiting for bcantrill, who actually has experience with large-scale production systems (unlike me), to expound on why he believes unikernels are a terrible idea, as he said in a brief rant here:
https://www.youtube.com/watch?v=Ya6h2zKlpaQ&t=5110