I mean obviously there would be some kind of floor in terms of how much range you are willing to be left with. If you're willing to discharge your car lower, you can take greater advantage of arbitrage opportunities, but obviously your car could be lower at any point in time.

You can control how much is given to the grid, and say that e.g. it has to have 60%+ left at all times.

There's no need to keep cars charged to 100% all the time. They already have batteries that are overkill for daily commutes, and if you suddenly need to make a long trip, you can top it up in 20 minutes from a highway charger.

BTW, on the Internet there's always some guy who just has to have a 500-mile daily commute while towing a boat, through a desert, in snow, uphill both ways. That's fine, they can opt out.

Note that the charging connector isn't a dumb plug like a household appliance. It has a two-way communication protocol that negotiates all of the parameters.

It won't drain below X% and will charge when below Y%

Potentially draining down the battery down to 80%