In Canada I recall that sort of thing being proposed, but it was shot down as one of the objectives they were trying to achieve was to prevent the conversion to be an excuse for companies to jack up prices by switching to a Smaller metric pack. Thus they wanted the conversion sizes to be a Clean Break, while still being useful for consumers.
Where they got into trouble was they also had the goal of reducing the number of different sizes sold so that consumers could make price comparisons without needing a calculator. They pushed standard sizes like 50, 100, 250 ml for toothpaste which got the manufacturers upset as they were quite happy to sell "medium" tubes that got slightly smaller every time the price went up, and bigger when the New-improved version at a higher price came out.
The industry push back came with some reason, they had standard package VOLUMES for detergent for example ( because consumers use it by volume) as well as standard weights as it had been traditionally sold by weight. In pushing back ideals like that a lot of the other changes proposed also fell off the table.
Perhaps the stangest conversion that others had mentioned was milk, which used to be in 3 packs of one quart, and is now sold in three packs of slightly larger bags (which still fit the bag holder) totaling 4 Litres, so each bag is 4/3 of a litre.