Is there or could there be a way to use the Model 3 to send power back to a home during peak power usage or during a power outage, essentially using the car as a wall pack as needed?
Not likely. Both Elon Musk and JB Straubel have shown little to no interest in the concept of Vehicle to Grid (V2G) or Vehicle to Home (V2H) operation. They haven't quite poo-pooed the idea (as I do). But I believe it is rather telling that neither Tesla Roadster, Model S, or Model X neither have offered such a feature... Even in the wake of it being portrayed as a 'plus' for what was the world's best selling roadgoing EV, the Nissan LEAF.
It is a future Tesla Energy product. Soon.