> would be a massive improvement

This is where we disagree. It would be a small improvement at best. Most of what you're pointing out are the awkward corner cases that just don't come up or, like you said, we already have other solutions for. Outside of some specialties, pretty much no one needs to know how many cups are in a gallon or yards in a mile or what a nautical mile is. I don't know those things, and I somehow get by OK.