Signup/signout & 'check if signed' up are available as Rule actions/condition
But we can't move users to a certain group yet based on a Rule Action.
This would enable us to put users in groups based on everything that we can reach with Rules like product purchases, Role, Profile, Userpoints, Link clicked, page visited, age, site activity, etc.
This piece of code seems to contain code on how to move a member to a different group through the Mailchimp Module (API):
and may be partly reusable