Why use self-selection or self organizing ways to form teams?
Besides handling the complexity part you get more stable teams faster, more motivated teams members and committed teams that lean towards each ready to compromise for making the team
Team collaboration over individual achievements
At ITU Copenhagen we agreed to set the boundaries at;
Team size 6 +/- 3 persons
1 scrum master
And some of the soft boundaries were focussing on the relationship between the students as the primary parameter and secondary calender gymnastic since the students only are working half time on this class.
Other parameters to consider was the areas of interest and wishes for learning objectives within this semester.
Great job by the self-selection workshop facilitators