Changing to 50 Hz would be very hard unless there was a 16.7% voltage reduction (although going from 480 to 400 is that percentage). That kind of voltage reduction would mean more current and more wiring losses. Or all those transformers have to be changed out. Keeping 60 Hz would be fine. Keeping the voltages we already have would be fine. Adding to it would be desired.
That much is easy- all they have to do is slow the generators 20% and you get both a 20% decrease in voltage and frequency, and that 480V 60Hz generator is now putting out 400V 50Hz! Pretty much every 3-phase emergency generator in production can do this, too - drop from 1800rpm to 1500 and that's about it, it's reconfigured from US to Europe. Most feature 12-tap coils that can be configured for 208V 60Hz, 480V 60Hz and 400V 50Hz. Often they can be derated for 208V 50Hz if required.
The transition, especially in residential areas, would be difficult. People love their NEMA plugs. Fortunately, the trend nowdays is that even though the cords have NEMA plugs, the appliances don't really care WHAT they get. I can't tell you how many different countries I've plugged a NEMA plug into with just a plug adapter- 100V 50Hz, 230V 50Hz, it all works. Sure, it all has to be designed this way, since a 60Hz transformer would saturate and burn up and an unregulated device built for 120V getting 240V isn't happy either, but just about everything is built for easy manufacture and export anymore.
