Crazy Pete does touch upon a valid issue -- which in my mind is one major impediment to conversion.
It is absolutely stupid to buy milk that comes in 1 gallon/3.7854 liter or 1 quart/0.9464 liter sizes. Nobody will put up with "decimals" like that.
If we are serious about changing, then we will have to change everything. Containers, product weights, etc. should all be re-sized / reconfigured to metric. Milk, as an example, should come in 1L or 4L containers. That means, of course, that crates will need to be resized as well. And when we buy gear and add up the base weight, we can brag about 2 kilo SUL -- no "decimals".
Yes, it will be horribly expensive... but also hugely effective. The way we have done it the last 30 years is also horribly expensive (cumulatively) but totally ineffective -- a waste of both money and effort with little results to show.
Take a "third world" country like Turkey. In 1924, their president decreed that the Arabic script be abandoned and the Roman alphabet adopted. His ministers pleaded with him to "do it in phases" -- there wasn't a single printing press in the entire country that could print in the Roman script! The president simply refused to budge. As a result, not a single book was published for an entire year. But then, starting in 1926, the whole country made the transition successfully. One year. That was all it took!
Amazing what one can do -- when NOT given a choice! We are a democracy. I say let Congress decide once and for all. Either we stay put -- or we make a dash for it. But once decided, we take no half-measures.