> Fixing this issue would require new remotely-operated breakers to be installed, which is costly, and it's hard to justify installing them proactively just in case.

No, the fix for this issue is that the inverter of your local solar installation checks if the grid delivers a 50 or 60 Hz waveform, and breaks if it does not. This is pretty much the standard in any installation today, and it's mandatory whether you declare your installation or not.

Side note, there is recently a push to vary the allowed deviation from 50/60 Hz a bit for each installation. The risk is that if all installations stop delivering at, say 50.1 Hz, then if the grid exceeds that value for some reason, there would be a very sudden drop in supply since all solar installations shut off at the same time.