That is only for the transitional period. What you would want to do is have a point in time where everyone internationally switches their date, hour, and second to match UTC at once. It might take a week for people to adjust, but really after that everything is so much smoother. I don't see it making much sense to try to use local time zones and UTC in tandem, which is the main reason it isn't catching on now, even though it makes more sense.