Energy storage is improving rapidly. Lithium-Ion batteries are but one technology that I don't personally expect will become the norm at grid-scale.
> The larger Powerwall was positioned as a longer-term back up power supply, which GTM noted was looking like a hard sell, with other market alternatives that were priced far below the $3500 price tag.
> The remaining 6.4 kwh device has less capacity, and is designed more to shift the load of available power, such as from a solar panel, to times when the production of such energy is lower.
There's nothing stopping anyone from getting more than one battery to make up for the capacity that was offered by the larger model.
Also the Powerwall is for home use. For utilities they offer Powerpacks, and they are already on sale: