Can you imagine the confusion? Having the same word mean a different amount of something would cause a lot of misunderstanding. Saying "This car weighs 2200 poundsm" have two different meanings depending on the year you said it sounds awful.

The new metric definitions work because they don't change the actual amount, they just change the way the amount is defined. (Natural constant vs reference weight)

We could gradually redefine pound to be closer and closer to kilogram, say, over a century, so that people don't notice. ~

That sounds like it would require more coordination than just adopting the kilogram as the primary unit of measure in a short period of time.

See ton vs tonne

Considering the speed at which metrologists create new standards, we'll be about three iterations into the infinite loop by the end of the century.

Nope, 1 pound should equal 0.5 kg.

It does in France already and has done for years, so when you ask for a pound of cheese you get 500g. Simples.