Great! Is there a visual indication that has occurred (see for example F1: https://www.racecar-engineering.com/tech-explained/f1-2014-e...). If not,
>You still don't want to cut through parts that can't be de-energized (ie do not push through the floor pan into your energy storage system).
You're right! That's why these things are standardized and labeled (http://www.solotogrouptravel.com/wp-content/uploads/2014/01/...)
>There is also a "first responder cut loop" which does the same, similar to the mentioned "RESCUE" lever on an aircraft cockpit.
The point isn't the function it's the labeling. As noted in other discussions (https://jalopnik.com/tesla-model-3-teardown-by-engineering-f...) of the model 3...there are no externally visible markers of where to cut until you open or remove panels and the markings themselves are unclear. The front first responder loop requires a 12V battery be connected to the vehicle if the frunk won't open under vehicle power.
None of this is about whether or not such systems exist...all of this is about the design and indication necessary of those systems in emergency situations. All F1 cars have different manufacturers...but they all have the same iconography and processes for disarming potentially energized systems (e.g., put the car in neutral, put out a fire, check if car is electrically safe). That commonality means it is easy to train first responders AND for first responders to know what to/not to do in an emergency.