At normal streetcar speeds, a full rollcage is a death trap. See, if a car crumples then it absorbs kinetic energy and spreads the impact over a longer period of time whereas a full cage passes more kinetic energy onto the squishy filling (that’s you) quicker. Not quite as bad as a full-on tube frame, but it takes just enough flex/crumple out of a normal car to cause issues.
The only reason we need cages in some vehicles is that those vehicles move as such high speeds that a side impact that would bend the bars on a rollcage would otherwise cause the door panels to meet in a car without one, just causing aforementioned squishy filling to squirt out.
As for the racing harness, it spreads out the impact force over a larger area, but that really isn’t an issue at mere highway speeds and thus not worth the added expense to the carmaker nor the added inconvenience to the driver. Besides, people seem to have a hard enough time figuring out the seatbelts we have now.
The HANS device is the only thing on your list that would actually increase safety at normal speeds, but considering how many people break their necks in accidents, you’re almost better off getting NBC shielding as that would protect you from a more likely hazard.
So, for a normal car, they have pretty much hit the point of diminishing returns so long as the speed limit is under 100 MPH.