Yes, as promised, we have more news from UDS-R, the Ubuntu Developer Summit for Ubuntu 13.04 (Raring Ringtail), due for release of April 25, 2013.
After we've announced earlier that Ubuntu 13.04 will be powered by Linux kernel 3.8, now it's time to tell you that Jason Warner, Ubuntu Desktop Manger, talked about the future of the Ubuntu desktop in an interview at UDS (see it above), saying that they will stay with the stable version of the GNOME desktop environment, which includes an up-to-date version of Nautilus.
Therefore, for Ubuntu 13.04 (Raring Ringtail), the developers will still use Nautilus as the default file manager, as they want something rock solid.
The current release of Ubuntu, the Quantal Quetzal, features packages from the GNOME 3.6 branch, but Nautilus is still at version 3.4, because of an incongruous integration with the Ubuntu desktop.
Hopefully, this will change in Ubuntu 13.04!