offloading all of that effort to the owners of the cars.
And eliminating a good deal of it, too.
The owners aren't going to be doing the engineering to safely house the batteries, nor will they be installing the monitor system to detect problems, nor becoming experts in the maintenance and electrical construction of battery systems. That's all been done already by the vehicle manufacturer, and the work has been paid for whether or not the company uses the batteries.
What's offloaded to owners is the cost of consumables, like the charge/discharge cycles mentioned here several times already. Then it's a question of whether the trade is mutually-beneficial. If six cars saves the company $4600, the company can pay the owners about $700 each year for about 250 recharge cycles. With that in mind, the cost of batteries (which I don't know offhand) and the lifetime in cycles (also unknown to me) will determine whether that's a fair trade. Sharing resources to reduce expenses might just end up being mutually profitable.
Your first point is kind of true, and kind of not. It's not eliminating any of that stuff at all...the cars do have to be designed to be safe, after all. But it's the owners of the cars paying the auto companies, in essence, to do that engineering for them. But the selection process of choosing a safe car over an unsafe one still resides with the owner. And yes, the consumables cost is entirely offloaded...and I would say, possibly increased also. The way in which an electric car in motion cycles its batteries is very different from how the cycling takes place when a car that was recharging flips over to become a demand response power source for a short period of time...and I would suggest that the car is optimized for the former and not the latter.