The issue with installing/storing apps/data to a non OS partition/drive is the same as using a slipstreamed image (AIK) or a backup... it is limited to one PC or OS.
In my mind I'm envisioning a quasi-package manager... where I could select which apps to have installed automatically in my absence, click go, and then it then becomes responsible for installing the specified apps in a correct order (based on dependencies), as well as potentially managing reboots.
Some (purchased) apps like Visual Studio or Office are large enough that they would be sitting on a network share, while other (often free apps) like Zune, iTunes or Paint.NET are updated often enough that a quick DL would be required first... so there would need to be a trusted list of the location of various downloadable apps that can be augmented by a local file store of software.
I know that Configuration Manager 2012 has a "Software Center" feature for enabling client PCs to request the install of specific bits of software... only I am thinking something far more automated.
I'm heading off to a 2.5 week vacation in Ireland come Saturday and had planned to see the sights, drink copious amounts of Guinness and Jamison and not do much of anycoding... hrm...