The powerwall use case will only grow when people get solar panels and when rural areas in countries lacking power infrastructure eletrify. But while that use case doesn't care as much about weight, bulk, charge rate and % capacity as car batteries, in return they are very sensitive to cost and the market will (depending on how cheaply recycling can be done) likely be filled with used car-batteries with degraded capacity.

If you invent a battery that is 2x as large and heavy as current vehicle batteries but half the cost, then you might think you would be able to sell them for stationary storage, but you are then competing with the price of second hand vehicle batteries which may well be half price already.