I would be sharing my experience of Building and Running technical communities for the past 20 + years ,
We had a similar discussion in the past PyCon India 2015 , we have grown many times since we last spoke about this topic openly , i propose the format of the disucssion as follows
There will be a panel discussion with representatives from all the existing drupal users groups or any FOSS groups. Where in we will discuss what makes these users group tick .
This i hope will be nice learning and sharing lessons to all the people present and who wants to start there own groups.
i have started jotting points here which will be the flow as well as the content of the discussion here https://docs.google.com/document/d/1TZxFvArSYkK3AA2RHDEaAq0GnQ5IMjzWImOmThBrMcg/edit?usp=sharing