This was already available as an aftermarket product available through the Priuschat forum, also there is an aftermarket DIY kit to do the same on older models.
The coolest application I’ve seen is someone set up their Prius up to keep their refrigerator operating during power outages in tornado alley. The second coolest application of this was the tailgating system at Giants stadium, guy had a blender and hotplate running off his Prius.
Actually many options, the Aims 1250 Watt Power Inverter seemed to be the most popular choice in Florida after the 4 hurricanes in 2004, which was the last time I thought about this.
http://priuschat.com/forums/gen-ii-prius-audio-electronics/10745-power-inverter-option.html
also people have built UPS systems in their houses to connect to their Prius, running separate electrical systems etc.
http://priups.com/riddle/answer-1.htm