The new regulation for the 'rapid shutdown' function, was driven by first responders for their safety, do you think that they may request that the rapid shutdown be installed on existing large commercial systems?
Once something is built, inspected and permitted, the AHJ does not come back and make them change it. I am sure that they could request it.
Insurance companies and owners would probably be the driving force for something like this, seeing how they would like the firefighters to put out the fire, rather than watching it burn out of fear of shock.
Here is an article that includes references to different methods of making ground fault systems safer with retrofits that people are doing:
As for people retrofitting systems with rapid shutdown devices, I have never heard of it. In California where Rapid Shutdown is not required until the 2014 NEC is adopted in Jan 2017, many if not most PV systems installed are not 690.12 Rapid Shutdown compliant.