This might be against the grain but...
What is the potential for a version that only focuses on the authentication? I have several sites that do not support open registration. That is, only known members of an organization are permitted to be registered. I would specifically not want any sort of user creation mechanism - the only thing I'd look for is the authentication piece so that someone registered could log in with Facebook credentials.
That's the purpose of setting "Create New Users" to no is to allow users to only log in through Facebook and not even have a joomla username and password... not sure if anyone uses that feature thoughIf I can tell them, "don't worry about remembering how to log in - just use your Facebook account," then that simplifies things.
Join our newsletter to get alerts for Joomla releases, tips and tricks and extension updates.