Earlier quoted context omitted.
Luckily, any degradation can all be predicted ahead of time. A 60kwh car battery might cost $10k, and allow 2000 charge cycles. So each kwh cycled into and out of the battery costs 8 cents. So a smart algorithm can decide it's worth draining the battery back into the grid if the profit to be made is more than 8 cents. Buuuut ... Delaying charging till later is free. So another car owner's car might see on the futures…
It worries me that if industrial-purpose batteries cost the same and have similar degradation, grid services will also decide not to charge/discharge if the profit is less than 8 cents. This tells me that Li-Ion batteries are far from the ideal medium for grid storage.
If it turns out people don't need all the cycles out their car battery then there's value in capturing that, but new large scale installations will move to other technologies over the next decade or two.