I like this idea.
Here is a use case I think Sloan would want to use.
The Instructor wants to divide the class into teams of 3-4 to work on projects. He sets up a group for each project topic and sets the maxium membership to 4.
For implementation, I would suggest not enforcing the membership cap too strictly. In general everything in education is subject to exceptions based on the instructors whim and it should be expected that the instructor will occasionally allow extra students in.
My first thought would be to have the logic that presents a join/request link check against the membership quota and change join to request if the class(or other type of dotlrn_community) is full.
Here is an example of why I suggest this implementation using the use case above
A 5th student presents the instructor with a compelling reason why he in particular should be allowed to join a full group. The instructor adds him through the control panel manage membership link and does not have to change the max_membership of the group. Thus, if another student in this group drops the class, bringing this group back down to 4, the project is still closed to new members.
Alternatively, the students in a specific project could convince the instructor that their topic was especially complex and needed a larger group and thus another person should be allowed to join. In this case the instructor would increase the max_members and if one of the existing students dropped out the group would again show as open for new members.
