I am well aware of some of the metric industries in the US. I've had both SAE and metric wrenches for decades - and there are still new cars that have SAE nuts and bolts on them, though I admit they are getting fewer. Still, to have them at all 25 years after they started converting is proof enough that it can't easily happen in a decade.
It makes a BIG difference when you renovate, I've done that a couple of times in my life. Matching pre-WWII 2x4's - that were actual 2x4's - with modern lumber was a PITA! They'd sell a lot of reducers as people tied 15 & 22mm into 1/2" and 3/4" copper water lines. Same problems matching old drains to new. 1200x2400 mm sheets are 3/4" short for the standard 8' wall as are 50x100x2400 mm framing boards. Sure, simple enough for new housing but with old housing you're dead meat. I don't know where you live but around here (and I'd bet in most of the Midwest at least) there are plenty of pre-WWII houses. Very few old houses are torn down for new subdivisions.
I guess you buy cheapie appliances, then. Our washer/dryer pair is 18 years old, we bought them when we moved into this house in '95. No overhauls or expensive repairs, though we did manage to get a quarter stuck in the interior drain hole, once, and that needed servicing big time because I couldn't figure out what was wrong with it. :-/ The dryer's drive belt needed replacing a few years ago. When we moved in here we were still using my parents old fridge from 1979 making it 24 years old when we replaced it - our daughter used it another year or two after that. My central A/C compressor has a 10 warranty and I expect it to last most likely 20+ years. The furnace has a 20 years warranty and it should last 30+ easy. They call this kind of stuff "durable goods" for a reason, you know - but you do get what you pay for. :shrug:
The countries that switched late did so when they were rebuilding after WWII. If we get invaded and have to rebuild half our country then it would be a great time to switch. Otherwise, it's going to cost lots of time and some extra money - or a decade of time and lots of money.