I suspect the team is already thinking about this, but I wanted to offer additional support for the idea.
It makes sense for a Vagrant box to be the primary supported installation, but I wonder if having Docker containers inside would streamline the testing process from the developers (who use Docker) to these supported environments.
It would also mean you wouldn't need to be building/supporting RPM (Centos) and APT (Xential and Bionic) packages, and the same docker containers would run on all the environments you support. You would only need to provide installation instructions for those environments for Docker to continue supporting them.
I note that Docker inside a Vagrant box is what FOLIO uses:https://morning-glory.docs.folio.org/docs/getting-started/installation/
Thank you for considering.