This is a really simple but elegant idea, and from a few other examples I’ve seen it feels very much like there are lots of fun ideas to explore in the space of flexible GPT-based APIs.
Your idea, for example, prompted an idea for a GPT-based recipe app. You just say something like, “provide a recipe for macaroni and cheese and add the ingredients to my shopping list.” Then you get a shopping list using your to-do approach.