Plastic packaging protects food from moisture and dirt. If you make the packaging out of a water-soluble material and then eat it, surely that's almost completely useless? Like, now you need some kind of additional outer wrapper to stop your edible packaging from getting contaminated. The article mentions muffin liners as an alternative use case, but those are usually made of thin paper and are already compostable.
I think the idea is that it becomes like fruit and vegetables. You purchase them unwrapped, wash them, and eat them. This would have implications on the supply chain of course to try and keep these items clean. It could also replace individually wrapped items, such as in a box of cereal bars the individual bars wouldn't need plastic wrap.
Not to mention how nasty the last one is when it takes you 2 months to finish a box... All of them exposed to air? Thanks but no thanks.