$0.50. That's how much savings one full charge/discharge can save you at current rates. That's $182 per year. Even people that plan ahead balk at a 5 year payoff, so you'd have to have the cost for a 10kWh battery be under $1000 to get people to buy in. Even $2k seems unlikely at technology and market levels.
Obviously those numbers change if the peak/off peak ratio changes, but $0.05 isn't enough of a difference to make it practical for that usage. Of course, it also functions as backup power or quite possibly can be used to increase the effective efficiency of renewables. I'm not trying to say that the system isn't impractical, just not economically sound for the on/off peak power shifting.