The sun would be the most obvious choice for such a reference point, though it’d be amusing to make it Greenwich and therefore make everyone deal with Earth’s rotation and orbit if they want extremely precise calculations (though I expect there wouldn’t really be a practical difference on that scale).
The thinking involved in driving a manual is very minimal once you get used to it, so I reckon any safety issues caused by that would be outweighed by a reduction in the unfortunately common situation of unintended acceleration crashes. You are lot less likely to drive through the nearest wall (or kids) if your instinctual reaction to moving when you should not be is to also go for the clutch and cut power instead of just pressing harder on the wrong pedal.