Tesla seems early in the grid storage market. Probably some companies are trying to come up with cheaper ways to do that. So, long term, I think cost will go down by quite a bit. Ten years from now, there will probably be a few companies cranking out cheap batteries for grid and domestic use that are optimized for $/kwh instead of kg/kwh.
Is that really true?
There a a LOT of lead acid batteries out there, considering there's been at least one sold alongside nearly every internal combustion engine larger than a handheld tool.