I was trying to run a similar arbitrage operation when the Tesla powerwall was first released but the breakeven was ridiculously long. Mine was to charge the powerwall when electricity was cheap on the grid and sell during peak. I found that a lot of the grids don't really support this kind of arbitrage at all and with the ones that do, the profit margin is so thin that it's basically not worth it.

As you say, Tesla is reframing the argument from renting your roof --> you selling clean electricity to the grid to make it more palatable but I don't see a problem with that.