It's been a few months since I managed to dig into Docker for some test projects at work, but docker0 was the name of the virtual bridge interface so probably the documentation you linked is what we're going on about :-)

I only started playing with Docker last December, and I think this was supported from that point in time, so definitely it could be a recent addition.

Currently I'm envisioning Docker playing a nice role in our CI and development infrastructure at work, where we can choose to start a new docker for any given project, and get a locally accessible IP back in a matter of seconds ... all from our soon-to-be-created CI+deployment web ui ;-)