If you have one guy spending 10 mins in every house on a street, he can probably fit GFCI's to 40 houses in a day. But that's only possible if it's a government/power company scheme. Installation could be even quicker and cheaper if it's installed internal to the electricity meter by the power company, and then you don't even need the homeowner home to do it.

Power companies have an incentive to add GFCI's, because ground leakage costs them real money, and those power flows are only 50% measured by the power meter (depending on the meter design). A 100 milliamp leak at 230 volts costs ~$30/yr or so.