[deccan]

Sure, the costs of switching over would be great, but at least it would be a one-off cost. Once it's done, you'd get savings from not having to maintain dual-measurement systems.

I think the main obstacle isn't economic but cultural. Suggesting the change to the American public would probably be political suicide to any U.S. politician. This isn't an issue championed by any large voter base, so no one would want to expend precious political capital on it.