A lot of that is doable now - like, how many grocery stores are even nearby to someone, so writing a custom bit of code to check the website of each, one by one, and looking for previously manually-identified items could be automated.

One major downside is prioritization of large chain stores at the expense of smaller mom & pop ones that don't maintain a constant inventory system accessible via the web. Someone could even volunteer their time to build them a database backend, but still they'd have to see the value in actually scanning the items every time or else it would quickly fall behind.