Tesla has already started incorporating stationary storage into some of its supercharger stations to help cut down on peak load. This is not just an act of goodwill, it actually makes economic sense for them, since it cuts down on demand charges from the utilities for high peak loads, as well as reducing the need for bigger transformers and such leading up to the station.

The electrical grid is already sized for peak usage, not average usage. Supercharger stations are also being sized for peak usage, and most of the stalls usually remain empty. Incorporating stationary storage cuts down on the costs incurred by both of these inefficiencies.