I may want a group of students in my class to share a private space in the wiki of the class, so that they can develop a project of their own before it is in a state that can be shown to the rest of the class (just to be read or also to be edited). In this way I could have several groups working simultaneously in their private projects.

If it were possible, when they are ready to share, that they can release the privacy themselves (without the need of an administrator), or inforce it again, or do that only for some pages, that would be even nicer.