While it sounds good, I can imagine some things which get in the way of the usefulness of this:
- Sharing works both ways, but it takes a family member 'slot' off both
- Worse potentially, secondary connections through your family slots get auto-added to your family (since everyone should be your family, right?). Therefore those ten slots could get swallowed up quick.
- Family members cannot be changed
- If one player is playing a game that is shared between family group, nobody else can play any other game from that same family list.