It's crazy that all the pieces have been there for decades but the idea that you should be able to talk about "the URL of this label (a document)" is nearly unfathomable for professionals who spend a huge chunk of their waking hours ostensibly building "the Web".
There's an easier way to do that: look for the label on the front that says "nut-free", or the label that says "may contain nuts" or "processed in a facility that processes nuts", or the primary ingredient that is not a nut, etc. No phone and app needed, no encoding data, anyone can do it, it's easy to find. Plus it's not easy to adopt a machine-encoding standard to changes in trends or society (like the difference between "contains nuts" and "processed in a facility that may process nuts"). We also already have OCR that can read all this text, and it's all laid out in a uniform way, so machine processing isn't that hard for existing labels.
I thought they could be useful for e.g. boxed lunches at a conference, or printed on a "mom and pop" restaurant menu, or in a cookbook, where maintaining a central database isn't really practical (aside from avoiding tracking).
It would also be easy to encode things like "Vegan" or "meat-free" or "contains nuts" which could be helpful to blind/low-vision folks or people who don't want to read through a 50-ingredient list to find out something contains shrimp extract or whatever.
I only got as far as setting up a domain (https://nut.codes) and a couple of aborted attempts at prototyping (https://github.com/nut-codes).