[rb12345]

You can actually do most of this today; you just need to have the metric equivalent amount at least as visible on the packaging and pricing labels to satisfy the EU rules. Milk is still sold in pints (technically some multiple of ~0.57 l, but near enough), some foods (e.g. jam) are still sold in 454g (i.e. 1 lb) amounts. All changing the rules does is allow you to remove the metric sizing, and I'm not convinced there's any burning desire for that. (The "metric martyrs" were largely against the additional work to add metric prices alongside Imperial ones; most places today no doubt use software to generate the price labels and will just keep things as-is.)