So, here's my proposed solution. Simply "extend" the groove that runs around the circumference of the top of the can so that it goes underneath the tab, thereby allowing the user ample room to get their finger underneath the tab. Sure, this may introduce some manufacturing complexities, but I can't imagine it's not possible.
Interestingly, Norman's four crietria for usable designs don't really tell the whole story, though: For the current design, we can observe the following:
- Conceptual model - good; the "perforated" edges of the tab over part that gets opened lets users know that this part is meant to be opened)
- Visibility - good; you can see everything you need to open the can easily
- Feedback - good; you know when you're [not] opening the can
- Mapping - good; nothing too tricky here
So, in the sense that the pop can behaves without any surprises, the design is usable; it behaves as we expect. But in the sense that we can't open the can, it's clearly unusable overall.