Regarding Circles + Chat: If you turn on chatting on Google+ it will ask you which Circles you want to be visible to. I'm not sure if this applies to all instances of Talk, and it looks like you can only say "I am visible to these Circles" (later configurable with the little dropdown next to the chat list in G+), but otherwise it seems to match what you're looking for.
You're right, to some extent it is what I'm talking about, however they state "People in these circles who also enable chat will be able to see when you're online and chat with you." and it feels like more of an all-or-nothing system (adding or removing Circles entirely from Chat).
Whereas Facebook's single-click 'on the fly' interface is superior to this - all groups always visible, one-click online and expanded, one-click offline and collapsed.
