In what Ubuntu release will gnomeshell become the default interface.
I think ... Never, it will be a desktop version of Unity.
I've changed this answer based on the new information that was released at the Ubuntu Developer Summit for 11.04.
For the foreseeable future, GNOME Shell is not be the default interface for Ubuntu Desktop. The developers are instead developing an expanded version of the Unity shell.
- Why is Ubuntu 11.04 switching to Unity?
- Will Ubuntu 11.04 use GNOME 3?
- Will there be a difference between Unity “Desktop” and Unity “Netbook” interface?
As far as I'm aware, the answer to this question is "to be determined".
It is my understanding that final decisions about the details of each release aren't made until the previous release has been completed. The release of Gnome 3 was delayed until early 2011 and Gnome Shell is not planned for 10.10 therefore a definitive answer must wait at least until after 10.10 is released in October. I would guess it will be a topic of discussion at the Ubuntu Developer Summit scheduled for late October.
I'd guess that since Gnome Shell will not be released until late in the 11.04 release cycle that Ubuntu will hold off from making it default until 11.10. There is a lot of integration that will need to be done to preserve the Ubuntu design work & apply it to the Gnome shell framework.
There have not been any published plans for setting it as the default, so at current it is impossible to say.