Delivery of application in a virtual machine now dramatically change. How easy could it be to create a virtual disk (App container) and install the applications in it. After that you add the user group to that container and real time the apps are ready for use by the user. Now with the acquisition of Cloud Volumes by VMware, the integration with VMware Horizon View is nearby. Q4 2014 it will be GA.
Even connecting a virtual drive to a physical desktop will bee possible in the future. The agent finds a virtual app container (could be a VHD file in Windows) and delivery directly the applications.
The basic image of a VDI desktop can be only OS. All common applications are placed in a Common container, user specific applications in other containers and even a user is local admin and has a persistent desktop, he has its own writable disk.