I wonder if technology from Better Place (http://en.wikipedia.org/wiki/Better_Place) was in any way an inspiration? They had developed a battery swapping system in 2007.
Actually, it's the other way around. Shai Agassi (founder of Better Place) visited Tesla several years back, then went on to found Better Place after what he saw:
https://twitter.com/elonmusk/status/347005150860283905