Once all manufacturing is controlled by China, they could refuse to make cars with steering on the right or use Standard measurements, increasing pressure and eventually forcing the UK and US to switch.
There are enough standards that don’t have non-metric alternatives like the square drive of socket wrenches or a lot of bicycle standards. It’s very unlikely that they will get replaced
Bicycles are hilarious because the same sizes will be designated in inches or millimeters depending on where or why they are taken. E.g. handlebars are 31.8 mm or 25.4 mm (1¼" and 1") but steerers are 1" or 1⅛". Wheels of the same diameter will be called 28", 29" or 700 (and the diameter is actually 25½" but it's only called "622 mm"). And even when they use metric from the start for something that is not a standard fastener already they end up with things like 28.99 mm spindles (not to be confused with 30 mm spindles, which also exist).
Thank you for informing me that China is likely to take over all manufacturing when it comes to cars. I am appalled that there are no US, Japanese, South Korean, Indian, Vietnamese, Russian, or any other nations that manufacture cars.
It also sounds completely plausible that a binary choice like left hand or right hand driving can be switched in a way that drives a pressure campaign that nations will give into China on because it’s an easier short term choice and wouldn’t gain an immediate reaction to due to the enormous cost that would be rapidly felt.
In the eastern parts of Russia (well even in "central" Russia like Novosibirsk), there's a lot of imported Japanese cars from their second-hand market. These have the wheels "on the wrong side", but nobody cares, they still drive on the right.
The US drives on the right (which is the right) side. So why would the US switch? Its really just Australia, Japan, India and the UK that drive on the left. The other 190ish countries all drive on the right.
PS Your 240V electric grid works that way because when the US switched to 120V (in like 1900 or so), we sold all our old gear to you and you never switched. So now all your electric things cost more as a result and your electrical outlets will kill you. So your decision making on such things is suspect.
The US has a 240 volt electric system nearly everywhere. The exceptions are some industrial factories that get higher voltage. There might be a handful of houses that haven't upgraded their electric system since the 1950s that are still 120volt only, but that is very rare (I've heard of it, but never seen it). We use 120 volts to outlets (120 is half of 240), but the system itself is 240 volts.