In Asia what they did was just redefine the meanings of customary market units so that they'd be instantly convertible to metric. For example, a Chinese Li 里 equals half of a kilometer, which is about equal to its old value of a third of a mile. That actually has merit, because most customary units are designed for use; you buy a quart or a gallon of milk instead of 500 deciliters, and a pound of flesh instead of half a kilogram.
The United States generally has no need to international metric units, as it is a large consumer market and the costs of internationalization would not be absorbed by the gains of compatibility, but if the United States were to switch to metric, it probably should mandate that a transitional system be used, with products legally mandated to indicate whether they are "Old Pounds", "New Pounds", and that the New Pounds / Quarts / Liters are defined in terms square with metric, so a "New Pound" would be defined as half a kilogram, a "New Gallon" would be defined as four liters instead of four quarts, a "New Quart" would be defined as a liter instead of its former almost a liter value.