It is not an "obvious bug". Google discontinued all of its own Chat clients. As far as Google is concerned, the service is defunct. In fact, all remnants of Chat/Talk settings have been removed from the new Google Voice web page user interface.
They've left the underlying Chat/XMPP protocol in place as an accommodation for OBi customers. Whether or not they clarify the wording of it, in a future update to the new UI, is unknown, although we've asked them to do so (for example, add a setting to enable or disable OBi support).
Your "household" scenario already works today: "Dad" is at work, and wants to call "Mom". Dad calls the household's inbound GV number, from his office or cell phone, which then forwards to, and rings all the forwarding phones. Mom answers whichever phone she is near at that time. If Dad is already at home, then he can either go talk to Mom in the other room, or call her from a real telephone number. Google Voice was designed to give an individual one inbound number, with the intended use case of people calling that number, to reach that one GV user at one of their forwarding phones. It wasn't designed for shared use.