I've been working on an installer for SteamOS with additional features like better support for SSDs, Kodi is installed by default along with a lot of other software, mouse acceleration is disabled and it allows you to record gameplay with a button combination on your xbox 360 controller to name a few. Yesterday I released version 2.0 of it.
For the people who are interested, I posted it here: http://steamcommunity.com/groups/steamuniverse/discussions/1/612823460253620427/
I'm downloading the ISO right now and will play around with it this weekend.
I'm guessing you mostly do apt-get's and copy over some default config files? Which would be easy to turn into a script that you can apply to any existing Debian based installation. You would not have to repackage the whole deal and waste bandwidth on a full ISO.
Have you thought about making this OS independent? The community could help out with porting the scripts to other platforms.
I think this is a great way to start a discussion about which software should be included on a gaming rig and get linux neophytes up and running quickly.
..."Which would be easy to turn into a script that you can apply to any existing Debian based installation."
It's not that simple. Firstly SteamOS uses a custom kernel, with the use of modified/optimised drivers in some cases.
Plus there's the constant client changes, experimental OpenGL translation layers, compatibility issues, not to mention all of the patches - most of which aren't public yet - covering the kernel/mesa/OpenGL etc.
You either add the alchemist repo, compile from source or install SteamOS - either way it'll never be OS independent.