Obsolete:Site-wide groups

Requirements

Please add concise descriptions of why you need site-wide groups here. There are quite a few different use cases around.

We want to put a whole class of people into a group so that we can easily enrol and unenrol them together from numerous courses. (If people leave that group, should they be unenrolled from the courses?)
We want to present a different theme to each group (with a common login page only). Useful for cases where one site is used by different companies. When combining this with the use of My Moodle then everyone sees just what they want to see, with customised branding etc. Is also useful for giving students a different view from teachers in more places.
What else?

It might be confusing to think of these as part of the groups systems we have already .... perhaps it's a different complementary system?

Let's call them cohorts and keep this separate from existing groups system.
Admin can use an admin interface to define cohorts (with name, icon, description, forced theme etc)
Admin can use the admin interface to add users to one or more cohorts (one person could be in Students, First Year Students, and CM3004)
Cohorts are visible in role assignment pages just like people, you can enrol a cohort in a course all with a particular role. A checkbox would allow you to choose whether cohort changes are mirrored as changed enrolments in future.
The cohort theme beats site theme, but is beaten by user or course themes.

We could do more, but is this simple idea enough for 99% of requirements?