i'm curious to know what the limitations of the technology are. Are the machine learning/CV algorithms not accurate enough to run it at scale?

I work with ML CV industrial systems, and they can certainly do accurate and detailed analysis and identification very quickly. The systems that do this are also necessarily very, very expensive -- much more expensive than any grocery store could possibly justify.

Of course, costs change with time, but right now I don't see how this sort of application could approach being financially feasible.