It doesn't help much in one public place. It helps a heck of a lot in 100'000 public places.
If Tesla can ever make a ~100kw powerwall-charger that costs $15'000 installed, comes with its own built in HPWC, and can be wired into any existing 208V/240V supply, things starts to make a lot of sense.
Then instead of 1 Supercharger station in a parking lot that costs $300'000 to build, needs a new transformer, and are subject to demand charges and what not, you can have 20 Powerwall chargers, distributed all over the place.
Put another way, Tesla wants to double the amount of SuperChargers before the Model 3 release. That's another 3500 chargers in ~600 locations. Instead, for the same price, they can have 70'000 "powerwall chargers" in 70'000 locations.
The individual chargers are not as nice as SuperChargers since you need to know which ones have charge available, and you probably need the logistics of reserving etc. But I wouldn't rule it out as an overall feasible model - once they can achieve a low enough cost for the Powerwall.