If you are setting up enough VM's that you need this you should have something like puppet installed and don't need this. If you are setting up one machine then do it by hand. Know the tools you have installed and keep track of them it will make deployment easier.
This isn't meant for huge deployments or rollouts. I use it to setup testing servers that mimic production boxes. And yea it should ready "setup rails with one line"
wget https://github.com/joshfng/railsready/raw/master/railsready.... && bash ./railsready.sh
Besides the "1" command is really 4.
If you are setting up enough VM's that you need this you should have something like puppet installed and don't need this. If you are setting up one machine then do it by hand. Know the tools you have installed and keep track of them it will make deployment easier.