In reality, you have the accepted world standard and the US one, with a small smattering of UK units thrown in. To argue the entire world should switch back to the US standard instead of the other way around is ridiculously obtuse.
The entire world switched to one country's system once. All of Europe used substantially the same system, and switched from it to one country's radically different system.
There's no reason it couldn't be done again. If it made so much sense to do one thing (of course, I don't actually think it did make that much sense: it was in the main driven through by governments seeking to radically break with the past) then surely if it makes sense to do something else, we all ought to?