The car is charging and discharging daily anyway. The key is just to do it at certain times.

If people can make serious money from the vehicles just from charging/discharging, there's also a big motivation to design batteries with longer lifecycles.

I mean, charging at specific times makes total sense, I totally agree (and there are currently (heh) ways to do that). But for vehicle-to-grid discharging, I'm not sure if the economics make sense. Someone smarter than I would have to do the calculus, but it's quite difficult to put a pricetag on the utility of actually driving the car.