It would be nice if it were possible to run steps inside a reusable docker container. The intention is to have different, clean build environments for every build, where dependencies could be installed without affecting the build host or other builds.

Further it would be nice if such a container would "live" throughout the whole build process and the user could decide which step to run inside it and which not (e.g. steps like sonar testing does not need to run inside the container, or maybe these tests should run in a dedicated sonar-container).

The "oki-docki" plugin uses "docker exec" to run commands inside a container which is a nice way of implementation. Accessing such a container from within the workflow plugin would be nice.
The "docker" plugin has dependencies on the docker image (e.g. it needs an installed jre, sshd , etc) which is not nice.