Video vs digital FDR
Before the usual hysteria starts about loved ones last moments etc it's a legitimate question. It all comes down to bang for the buck.
Some of the "demand" for this comes from the NTSB and was prompted by a few specific crashes.
One point is expanded digital FDR is happening and uses existing "infrastructure" and a lot of acquired knowledge. I do not think digital FDR was available the two 737 crashes that are suspected rudder events. I'm not sure of the other events you refer to.
In the silk air case it seems someone with knowledge was able to disable the FDR and CVR and presumably would have done the same with a video recorder. I suspect a bit of gum and paper over the lens might become standard preflight if they were installed.
If video were available it will take at least a few crashes to figure out how to optimize the equipment, installation and the use of data. As crashes are relatively rare this will be a long time in providing any real benefit for what is sure to be a significant expenditure. Improved ground radar and signage might be a better place to spend money.
Getting people to stop driving drunk and use their seatbelts would save a lot more lives than cockpit video ever will.
20driver