You can learn a lot from the StackExchange model.
Members create their own communities. They have to meet a critiera for further support. StackExchange provides advice/expertise. They share best practices. They kill the groups that aren’t taking off.
Have a criteria for members that want to create their own space in the community.
For example, if members want to create their own group, write a regular column, host/organize a live event, establish a poll for a community, you can set clear guidelines. These guidelines might state that they need 50+ interested members, 20 some interesting talking points/questions, a goal/purpose for the group and a pledge to commit to making it happen.
This is a smart social process for scaling activity in your community. You can share advice, best practices and manage the sub-group leaders. You have members contacting each other (good for building relationships) to run groups/host events etc…
It takes you out of the process – which is a good thing. Activity in a community should be as independent of you as possible.