Re: External Blogs
regarding the admin management of the external blogs, the plugin could be built with moderation capabilities for the site admin. Ie. site admin is notified when a member adds an external blog. They check it and ban it (disabling its output and visibility) if the content is offensive. In this case a member may have to request an un-ban with another URL…
As far as just specifying the external blog URL goes, this could just be an extra profile field, no additional effort needed.