My carpentry experience is limited to relatively small DIY projects, but one thing leads me to doubt that metric is "absolutely unworkable:" Don't people build with wood outside the US?
But according to an article in Van Nostrand's Scientific Magazine, "A Comparison of British and Metric Measurements for Engineering Purposes," a report of the proceedings of the British Society of Civil Engineers, by Arthur Hamilton-Smythe, BA, (you can google it - it's highly amusing) the writer was in France and dealing with some railway matter or other, and the French engineer pulled a two-foot rule out of his pocket!
"Here's a health to every learned man who goes by common-sense,
And would not plague the workingman on any vain pretense.
But as for those philanthropists who'd send us back to school,
Oh, bless their eyes if they ever tries to put down the three-foot rule!"