Can't wait to see what you will bring out. Exciting times.

I was literally just posting to marky a few minutes back discussing these subjects and tribes.

For me a tribe would need a light account for new users until the find their feet.
Multiple sign-up options. Facebook, email, google, twitter as standard.
An introduction phase with tutorials for getting started.
A curation team to find, encourage and engage new users until they grow a following or find their feet.
A help team to contact and ask questions on site.

From the tribes side they would need marketing and advertisement. People won't join what they can't see or understand quickly. Once you can get people into the eco-system through a tribe they will fall into other parts fairly quickly as a lot of content spans across multiple tribes and talks about apps in the system.

I will be watching eagerly to see what gets released and hope to join into it at some stage.