This would also be useful to address a pet peeve of mine when reading recipes: calling for "1 can" of something. I'm always careful to annotate "1 15-oz can of ..." in my recipes, but there doesn't currently seem to be a good way to write this. @tomato sauce{15%oz} reads poorly because it seems like you need to measure it out, @can of tomato sauce{15%oz} makes that a little clearer, but "can" really wants to be part of the unit, not the ingredient. And @tomato sauce{15%oz can} is also weird, and you might end up with a shopping list calling for a "44 oz can" or something strange like that. Instead, I'd like to write @tomato sauce{15%oz, 1 medium can} (or maybe the other order) and see the recipe rendered as "1 medium can tomato sauce (15 oz)" or such like.

This is very important, and my biggest issue with cooklang so far. Many good baking recipes are written with both volume measurements and weight measurements, i.e. 2 cups (260 grams) flour, since it's much more accurate to use a kitchen scale and measure by weight, but you want to include the volume measurements for people who aren't used to baking that way and might not have a kitchen scale.

Also, if the recipe only has volume measurements, then I'd like to be able to add weight measurements without overwriting the original recipe.

We already have | pipes as synonyms for items in the shopping list spec, I think it'd be great to use for the same thing within braces too:

Boil the %pasta{1%cup|200%g} and…

I think commas are more useful for another purpose, specifying pre-prepared state:

add @green chilli{1, finely chopped}, @shallot{} or @red onion{1, finely chopped}, and @coriander leaves{1%tbsp, finely chopped}