I know I'm not the only one who has this problem. Has anyone figured out a solution?
We implemented something like that, but instead of a feed you have medical records. RBAC might be overkill for your purposes, however, unless you want to give your followers specific permissions on what stories in your feed they can view (i.e. you can use tags/keywords to exclude certain viewers; "sex", "boyfriend" or "one night stand" would block your parents and family members from seeing that particular story, etc.)
About a day's work if you have done it once.
[Correction: this is just for one feed, one you control yourself. For every possible CMS, blog engine or host, you would need the same as well. You would also need to setup a central OAuth authorization service for all the consumers.]