The Ubuntu Tech Board approved last week that Ubuntu GNOME is now an official flavor/derivative of Ubuntu Linux.
As some non-Mir news, Tim Lunn of the Ubuntu GNOME project wrote into Phoronix that the OS spin is now an official Ubuntu flavor. Ubuntu GNOME was originally released last year in conjunction with Ubuntu 12.10, but now the flavor has been approved by the Tech Board per the IRC meeting logs
The Ubuntu GNOME flavor seeks to be a "pure GNOME" desktop experience rather than Unity while building the rest atop the Ubuntu stack. "Our first release for 12.10 showed that there was a strong demand for a great GNOME experience on Ubuntu and we are now working towards our second release based on Ubuntu 13.04."
With now being an official flavor, daily release ISOs of Ubuntu GNOME will come out. Though a shortcoming of Ubuntu GNOME 13.04 is that it will be using the older GNOME 3.6 release and not the imminent GNOME 3.8 desktop due to the Ubuntu packages sticking to the older packages. However, a GNOME 3.8 PPA will be available.