I thought most of chocolatey was based on powershell. I will need to play around with it.
For mac and linux I will be using mono to build. And it's pretty easy for them to install ruby even without the script, it just seems like most windows users don't want to install ruby. So for now PrepareBuildEnvironment.bat will be specific to win users.
For other OS there will just be an info in readme.
I guess the bess would be to create a chocolate package called 'ruby-portable'.