Price per kg, or liter or unit - according to European Laws
In many countries the law requires to show the price on items like powder in kg, with any liquid in liters and pills or tablets in units. If you want to sell products like protein powder, whereby the package is 750g, you have to show the customer the price per 1kg. This is not a "nice add-on", this is law all over the European market. It is very tricky to add a field, because these fields can not calculate and if the price changes, there is a lot of work involved to keep track. The authorities in Europe are looking into this subject and there is a high risk of getting heavy fines if the online shops do not comply.
I don't know if this should be in the core system or as an add-on, however it is just a very simple operation and only a few fields have to be added and WooCommerce complies to European Trade Laws.
I agree 100% with you, it should be included in any e-commerce sw.
Besides this been part of European Law this is also good for customer transparency. So it is always a plus to have!