As I recall pounds and ounces were overtaken by the Common Market.
Not really. Metric mass units were used in science long before I got to secondary school. Even Pounds, shillings and pence eventually got metricated, but not 'common marketised'.
Yes, I have used Btu's, ergs, dynes, calories and a few other older units, but metric is sooo easy compared to gallons, quarts, pints, gills, etc. One thousand (10^3 ) kilograms to a metric tonne is far better than 20 hundred weights (actually 112 pounds!), with quarters, stones, pound and ounces to follow on - so multiples of 20, 4, 2, 14, and 16. Even the Troy ounce was sort of metric - 30g instead of 28.3 g for the Imperial version. The series of units has changed several times over the years, but the SI system is now universal except for everyday use in the US and a few other outposts.
Think how today's students would get on with calculations! Think how much more complex the lowly calculator would need to be, what with British Imerial units (and some US measures of the same name).
No, the only fixed unit which might be regretted in the future is, I reckon, the velocity of light in a vacuum. As they delve deeper into sub atomic particle layers there may come a time when the macro and micro ends of the spectrum don't quite tie in together.