I would like to see metric building standards happen. It would require a bit of a transition period but just get it done. 1 foot is very close to 30cm, so the changes would not need to be that big. It would make CAD stuff so much easier if everything was metric. CAD is a pain in the ass with imperial, how do you represent fractions when computers work with decimal? Though I typically get around that by just making everything in inches, typically I don't need more precision than that if I'm building something big. For small stuff where I do need precision than the standard lumber dimensions (ex: sheet of plywood being 1/2" thick and 4x8 feet) matter less since I'm cutting stuff to more precise sizes anyway, so I use mm. It's easier in my head to know that 10mm is 1cm or 1000mm is 1m etc. I don't even need to think about it. But with inches and feet you end up with fractions and you're constantly doing math in your head.
Pipe sizes are annoying too, would be nice if all that stuff was in mm. So much easier to know immediately what size is bigger than another by just looking at the number. It's not so bad with the very standard sizes like 1/2" and 3/4" and 1/4" because I just know them off hand as they are standard and I can just visualize them right away but when you run into the more oddball ones it requires more thinking to figure out the size.