This used to be a feature on the site however was disable. If i remember correctly it will be implemented in AG3, or was at least under consideration last time i checked.
Yes, this is currently in AG3. The dot under your avatar will show up as a green light if the user is currently active. If not, the message will show when that user was active. If the user has been gone for quite a while, it will (currently) say "Presence is currently unknown".
