We already do mix them in the US. I have two full sets of hand tools, because I need to have both SAE and Metric tools to fix things. I'm a photographer, and camera lenses are all metric focal lengths, and have been since long before I was born.
Milk is sold in pints, quarts, half-gallons and gallons. Booze is sold in 750ML and 1.75L bottles. The weight on the front of packaged foods usually list ounces, but the nutritional labels on the back of the same packages list protein and fat in grams.
I personally have no problem cooking from a recipe written in Imperial or Metric measures. My measuring cups and kitchen scale can measure both.
As mentioned before, I do prefer F to C for temperature, but I have an app on my iPhone to do the conversions instantly, so I can cope with either, if I need to.
CD