That went into the 70s - when I was in school we learned both metric and imperial because the USA was in the process of switching. Wish we had followed through...
I don't think it is impossible, and many products wouldn't seem to change at all. 2L of milk visually looks like about a half gallon. (I am American and moved to Norway). Canned goods look to be around the same size. And so on.
Speed limits would take a bit of getting used to in some older cars, but I think most newer cars with digital dashboards would just switch over. Buying gas would take a little time, but it'll work out. A meter isn't all that different from a yard and rulers are cheap ways to measure centimeters. Signage and things will help folks do the conversion.
Temperature and distance, however, will take a bit longer. It has taken me a while to really understand how warm 10C is without having to convert the temperature, but I'm sure we can communicate such things. I still have no real handle on how far 100km is nor how long that would take to drive, though I know it is too far to walk.
Mostly, it would take legislation and money to start changing things (signs, for example) over. This would need to happen in 2 different stages so that for a decent time, both would be shown. Some things would just be immediately updated without issue.
Some of the sticker things probably needs to be funded as well - such as gas stations. I don't think they'd need to replace the entire pump, but it is a possibility especially for older stations.
Oh, and again, legislation needs to be there. In the current political climate, this is going to be a real hurdle and I can imagine it taking a patriotic tone much like the debate of teaching cursive writing.
Late 70s, I think (Carter administration). I remember those. As a kid I wondered, "will they put in kilometer-marker signs like the mile-marker signs on state roads?" (the small white ones near road level).
The only people that think it's painful are the folks who keep telling us we need to switch. We know the measurements we use pretty well, and even then there are plenty of things already measured in metric.
Plus, it's not like everyone else has fully switched. The UK still seems perfectly comfortable talking about weight in stones and all their cars measure speed in mph just like the US.
Yes nearly every country is in some sort of hybrid state. In Europe you have the UK with one foot in the empire, but other countries also mix in e.g inches for tv’s, car wheel sizes and so on. It’s almost not a measurement, it’s more like a size scale (you don’t measure your wheels in absolute terms but you know what 19” rims look like compared to 17”). Ironically we put mm sized tyres on these rims.
I think the US should try to switch one area at a time. Just like we will eventually measure Tv’s in metric (Australia does already I believe) the US could probably ease into metric by adding more and more areas that use it.
At one point TVs were in centimetres and computer monitors were in inches, but now they've seem to have given up and sell both in inches (which is probably against some regulation somewhere).
I lived in Australia in 2002 and was surprised to see things like TVs be marketed in cm. Did that change? Makes sense to use the same marketing as manufacturers since model names will have inch sizes in them.
All screws here are metric, except for PC computer cases, harddrives etc. And screens, as mentioned. Everywhere the US influences global technology, the imperial units show up.
In the UK the metric system is used in business, construction, science etc. Really anything serious.
Imperial measures seem to persist informally for things that are difficult to visualise, like body weight or speed. Or things that are customary like a pint. I will ask for a pint because that is how much beer I want to drink. Not because I actually care what unit it is in. And young people haven't got a clue how to add up pounds and ounces or inches and feet.
That's because their main commercial partner (both because of geographical proximity and shared language which allows using the same packaging) isn't fully metric.
It used to be the same in Canada (or at least Québec) but I've heard that more products are sold in round metric quantities these days.
Nearly all the butter you see here is labeled Irish, as is most of the other dairy and meat. The north has the opposite, most of the meat/dairy is labeled from NI. (With the exception of some of the branded stuff, like kerrygold butter which is available on both sides of the border. )
There was an attempt in the 60s to convert to metric in US. If you are in SF bay area, go check this out:
https://images.app.goo.gl/JBqNpATVWgwi2qFh8