Can you elaborate on your first use case - for what kind of embedded development do you use virtualbox and how?

Regarding your second point - you can either attach a shell for testing (e.g. I often build a Dockerfile first interactively via /bin/bash inside the container) or use the hammer (a web-UI) and connect your localhost to the docker network interface.

Data exchange between host and container is also simply done via bind mounts - which might be more elaborate in production however.