Yup, it has happened. The second hack for the Canon EOS 5D Mark II has been produced and demonstrated. Same author, different feature. This time, audio metering. Here's the demo!
Demo of the audio level meters in the 5D Mark Free (version 0.0.4). The audio is calibrated from -40 dB to 0 dB with 5 dB tick marks, but the ballistics are not good and drawing to the VRAM is not synced with the redraw period. Despite those problems, we're running our own code on the camera and showing that we can add new features to it.
For more details see the forum post: cinema5d
Hudson's first hack, Audio Gain Control, was discussed on this blog as well.
As far as I'm aware, neither of these has been released to the public, only demonstrated. I'm dying to see what Canon's working on!
(Photo credit: snap from the video)