Lots of things wouldn't need to change initially, other than labeling. A 12 Oz soda becomes a 350 mL.
You think electronics, mostly designed and manufactured overseas, are made in English units or metric? I'm guessing metric and they then get slapped with approximate English measurements.
The HVAC industry would have one of the hardest transitions, but mainly because sizing equations and rules of thumbs are so ingrained in the end use engineers and designers and not because the mfgs aren't already making metric units for global sales.