I would assume that the most basic use case is one car, one driver... Nearly every person I know that would care about having a device like this meets these criteria.
How, exactly, would you expect it to work with two phones in the same car? It's not like it could tell which of you is driving...
I guess my argument is that it is likely less 'basic' than you think. Having two people share a car, and both interested in accessing their data, sounds like an edge case.
I imagine that it'd be easier to either get rid of one of your accounts so everything goes to one single account, or have multiple plugs, and you swap out based on who is driving.
Also, I got a discount as an original kickstarter. You should check your email/spam folder to see if you got one as well.