I think they mean the classic install process of "curl -s <url> | bash", used to download and then execute a bash script. The real question in my opinion is what kind of tools can fully set up an entire environment, including sessions, from a bash script? Homebrew only gets you so far.
Apologies for the self-plug but this is what I built for GitHub to do exactly this: https://github.com/MikeMcQuaid/strap. Add Homebrew Bundle and a Dotfiles repo into the mix and you get what was described. This is obviously pretty Homebrew and GitHub centric because I work on both.
I haven't played with it on my mac, but I've been headed down the path of setting up my environment with Ansible. I have one script that bootstraps Ansible, and it does the rest. That said, I haven't managed to get everything in there yet. It requires discipline to never set things up without putting them in configuration management (same as if you're configuring servers).
Some of the old Boxen libraries (Puppet automation for things generally outside of the "run a command to install" area--like complex OS configuration and per-application setting installation) plus a bit of bash and a few Hammerspoon scripts gets me working. It's not pretty, but usually means the only things I have to do manually are install XCode and log into a few accounts (unless I'm changing hardware types or OSX vesions).
Possibly a complete image of the disk. dd'ing from an SSD with trim gets you zeros for the unused sectors, otherwise write a big file with zeros on the remaining space.
This data compresses quite well and gets you all the hidden and extra attributes an rsync might miss. That would be my unix-y approach.
