Before I made the switch from Rdio to Spotify they (Rdio) came up with a pricing model that allowed families to purchase a slightly discounted subscription.
$9.99 for single unlimited user
$17.99 for 2 family members (20% discount)
$22.99 for 3 family members (50% discount)
Would love to see a similar pricing model so the rest of the family could get in on the action!