And again, back to the issue of the pax actually wearing them. As flight crew we are trained in how to wear our seatbelts properly... pax are not. Even when you tell them it must be worn "low and tight" they still don't wear them properly (if at all) I would hazard a guess that at least some of the Asiana injuries would have been from seatbelts worn too loosely.
Then the other problem you have with a harness (even for takeoff and landing) is wearing it properly. It has to sit over your hip bones with the buckle in the correct position or you risk causing more damage than its worth. Given that half the crew I fly with don't even wear it properly (and this has applied at every airline I've worked at) then hoping for pax to do it is probably too much to ask....
Pillows will end up everywhere (you see a few in the photos) personally I have mine on my lap ready when a pax, just in case... not sure it would help much in fact you'd need to be careful that it's not going to change the angle of your neck too much but could be helpful to cushion the back of your head against flying debris...