Sorry to rain on your parade, but the TWA accident was at night so I'm not sure a camera would have shed much more light on what accident investigators already know from analysis of the wreckage.
With regard to the TV in the cabin, I'm sure that any halfway intelligent hijacker would be able to locate them and put a wad of chewy over the lense. Even if they didn't, it would not have averted september 11 (at the time) as authorities already knew the planes were hijacked.
Prevention is better than cure. Fact is, september 11 would not have been possible on an El Al aircraft (strengthened double cockpit doors).