It makes too much sense for everybody to use the same system.
In reality it makes no difference if your speed is knots, MPH or K's.
The Yanks have a hatred for anything metric, using furlongs, bushels, rods, ounces, acres, chains makes so much more sense đ
Makes hard work and room for error in the likes of Canada where they are supposed to work with the metric system but the rednecks want to be Amerrycarn and have a mixture of US and imperial measurements and the products like fuel and chemical are supplied as metric recommendations.
I wouldn't have any problem with using K's for speed, metres for height.