I think the only possible way to effect such a change is to mandate a complete and clean switch (eliminating English units and completely replacing with Metric units) at a specific point in time. If that were to happen (which in itself is unlikely), then there would be an unprecedented amount of screaming and gnashing of teeth, and whoever politically supported the mandate would be quickly tossed out on their rears... and the mandate would quickly be overturned with the replacement politicians...
IMHO, I think the vast majority of US citizens couldn't give a hoot about the system that the rest of the world uses, and so have absolutely no desire to change it. There's basically no benefit to the average person... they (or should I say 'we'?) inherently know how long a foot or a yard is, how far a mile is, how fast 60mph is, how heavy a pound is, how much a gallon is... very few know (or care) how long a cm or meter is, how far a km is, etc.
That said, I personally prefer metric as well, and have no problem going through the "pain" necessary to switch over... but I'm not holding my breath expecting it to happen in my lifetime...
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