Grid battery storage would have to fall in cost far more than expected to be practical. Goldman Sachs analysts don’t see costs falling by more than a factor of 2 for the foreseeable future.
This analysis only looks at vehicle batteries, but there are a ton of technologies that aren't suitable for vehicles that _are_ suitable for the grid due to weight concerns and a lot of them have room to become significantly cheaper than lithium.
I just don't think the grid storage market is going to be leftover vehicle batteries. The demand will be big enough that battery technology will be tailored toward grid storage; cheaper batteries that are less dense, super-high lifecycle numbers that cars don't need, less need for high charge and discharge rates.
Seasonal storage is another issue all together. Also, very northern latitudes may be better served by nuclear power.