It might make more sense to get a Powerwall if it becomes cheap enough. The batteries that go into a Tesla car are the same batteries that go into a Powerwall. This implies that improvements in battery cost posited by the article will mostly likely apply to Powerwalls as well as to cars.

A Powerwall would be always available. What if your car isn't there when there is a power outage? What if your car isn't there when you are collecting solar energy? You wouldn't have to lose power when you drive your car during a power outage.

A Tesla with this ability could definitely serve as a supplement but the cheaper batteries are, the more it makes sense to have one permanently wired to your house. This ability would be an interim technology assuming battery costs go down enough.