"Going metric" raises the question of whether we adopt metric measures for our existing standards (such as pipe threads) or actually adopt the ISO sizes. The latter would cause a brief but massive inventory management problem, that nobody's ever willing to put up with, even if there's a long term benefit.
I believe we made a mistake in how we tried to teach the metric system. I learned in first grade: Metric is easy because it's just math. Most people heard "math" and freaked out. Metric was taught as a bunch of conversions and units. Inches were taught as: Here's a ruler, go measure some things.
I remember talking to a machinist, and he said: "I hate the metric system because there's so much math." That was 30+ years ago. Today, machinists just read mm or inches from the same digital readout or CAD program.
My Canadian friends learned metric as: Here's a ruler, go measure some things.