That's a tricky question. There are too many problems with adopting the system, it is happening, but will take a long long time. The US auto industry has adopted metric fasteners for the most part. There are a lot of meanings to "the metric system". The US will probably never go to metric road and highway signage. Selling stuff by the kg or liter? Or gram or meter? They do sell soda in one, two and three liter bottles. Booze bottles are metric measure (in NY, not sure of other states), beer is still imperial measure. What about engineering or technology or manufacturing? If you are an offshore company buying US made equipment such as heavy machinery or machine tools, and you want a metric machine, no problem there at all, we do it every day. There is essentially no difference in price between imperial and metric standard parts such as steel and bearings and common machine components. When we all agree that we want our road signs and weights and measures and temperatures to be metric, then it will happen. It will be a long time before you pump 10 liters of gasoline into your truck (with the 5.7l engine...auto industry) that gets about 8 km/l and burn it up going 80 km/hr down the highway, hauling your 8 meter long bass boat that weights 1800 kg, to hit the ten square kilometer lake trying to tease out that 750 mm long bucketmouth on that beautiful sunny day with temps in the lower twenties (Celsius of course).