This is a year old but it does sound like Tesla has been researching vehicle to grid possibilities:
Tesla executive hints vehicles will soon drive the grid
Honda had a device which would allow owners to tap into their car's battery for V2H:
Honda Power 9000 Lets EV Owners Power Homes During Grid Outages
I would be interested in an officially supported V2H solution myself. I wouldn't plan on using it regularly but would be great in emergency situations. While I don't have to worry about hurricanes, we have had ice storms which have cut the power for day. With a V2H solution, I could power my boiler (and thus heat the entire house) and not have to worry about the pipes bursting.
I agree that Powerwalls can be expensive if not part of a solar system but I should be getting some Powerwalls thanks to the referral program which makes them very affordable for me. I'm going to have those installed before solar but the ability to send power from my car back to the Powerwalls (as
@Ben W mentioned) would be a great solution to keep things running for days, if necessary.