I just saw this topic and want to add my 2 cents.

My previous company is working on this very project. Introducing video/audio recording to the cockpits of commercial airplanes.
The problem is not with the cost of using satellites to stream data. The problem is with the limitations of hardware and bandwidth.
We've done several tests and at this point of time, it would be humanly impossible to stream data from all commercial airplanes. And we are talking only about 3 cameras installed in the cockpit streaming 3 to 5Mbps video (don't confuse it with MegaBytes).

What few companies are doing right now, is to introduce cameras to the cockpit and store the data locally in the box similar to the black box. In the case of accident, video box will be recovered from the crash site and then recordings will be evaluated. This option is cost effective and is easily doable.
Also, pilot unions will be happy. The video will be recorded constantly but only downloaded in case of incident/accident.