Canonical has stated an interest in providing a way for Ubuntu users to gracefully switch over to Gnome Shell, disabling Canonical specific technologies to give the user something as close to the intended Gnome experience as possible. Maybe through an environment variable setting, or some other easy to use means. First I want to say this is commendable attitude.
My question is, is Unity engineered such that when other linux distributors, who are shipping nearly stock gnome, may want to provide Unity as an alternative interface to their users to choose from among many other options, will that be possible using stock upstream gnome technologies? Or are there a set of yet-to-be-upstreamed patches developed by Canonical to existing gnome components that would also need to be integrated by other linux distributors for Unity to work as anticipated?