Debian developers will rely upon Popcon package statistics in the year ahead to see how many people install GNOME over Xfce, the state of accessibility support, and the UI work-flow for both GNOME and Xfce in determining the default Debian desktop. Additionally, if any CD size constraints come about with GNOME packages, Xfce then has another advantage.
For now, Xfce is back to being the default Debian desktop environment but GNOME along with KDE and other desktop choices can be easily installed from the Debian archive. This is a change to happen for Debian 8.0 Jessie that will be frozen next November and likely released in 2015.
The change of the default Debian desktop environment happened with this Tasksel Git commit.