The xStorage has numerous benefits: it can store energy during off-peak hours when it's cheapest, and customers can resell the stored energy back to the grid when demand is high and costs are up. The battery pack will be completely integrated, and it will also have smartphone connectivity for ease of use. Naturally, Nissan will expect customers to power up their Leaf using the xStorage, and it's more likely to be installed in a garage instead of the living room.
Designed together with Eaton, the xStorage is currently being marketed to European customers only, with no concrete plans to bring it over to the US. But with Tesla's Powerwall on the market, it's likely that US customers are constantly on Nissan's mind, depending how xStorage sales go in the EU.