For what it’s worth, there is such a thing as the United States Metric Association, doing what they can to encourage more full use of the metric system – which really is not much beyond advocating for it and providing educational materials where they can.
Um, technically, the US is on the metric system; all of the ‘normal’ US measures are legally defined in metric units.
As far as the wood sizes are concerned, I asked on this board a while back what the Canadian practice was. One or two Canucks said that the plywood sheathing they use is indeed 4 foot by 8 foot: it’s not like they themselves can hope to overcome the inertia of that great big lumber market to the south. Frankly, I expect that many lumber sizes will remain the same for a long time, no matter what they’re labeled.
But I think the US is making slow progress in greater metric usage. Oh, here’s a slightly confusing one; I’ve seen that diving tank pressures are typically shown as ‘bars’. Well, that’s metric, sort of, but not official. One bar is 100 kPa, and coincidentally, pretty close to one standard atmosphere of pressure.
Anyhow, no cite available, but I’ve seen a few news reports that casually use some metric units without trying to back-convert them.
The military is metric, mostly, I believe. International sports are metric, of course, as well as a lot of sports equipment. Hair care products are metric, as is medicine, of course.
I expect that the US will continue to slowly bring in more metric usage without officially abandoning the traditional units. Hey, if we can deal with the mess that is English, what’s a few extra measurement units?