I always thought the rule was about damage (liquid spilling onto your bag and other passengers' bags) rather than safety? That's based on how the rule was shaped: 100ml containers with no limits as long as in a sealed plastic bag.

I wonder if they'll walk this back? If you put a 2L water bottle in the overhead compartment and hit enough turbulence, it could open and drench the entire compartment and other people's luggage.

You're already allowed to refill large water bottles from a water fountain after passing through security, so the situation you described is already allowed to happen.