Probably need to discuss how to isolate the component's Javascript.
Web component's JavaScript exists in the global scope so it can overwrite and be overwritten by scripts external to the component.
This is actually a major issue in my opinion. You can isolate your code to some extent using an IIFE but if you want to include 3rd party libraries that quickly becomes very hard to do. 3rd party libraries will also often directly modify the window object making any isolation attempts ineffective.
Pretty sure ES6 addresses this by isolating all vendor libraries to the level of the module where they're imported. SystemJS[0] emulates this behavior with relatively few caveats.
The module tag is not es6, not even worked on by the same standards body. Futhermore, while there is consensus that a module tag would be nice, no one is actively working on it. So don't depend on it in this context.
Nobody ever bothers to think of surfacing the API in machine-consumable way. At least Polymer exposes attributes at the top-level tag, but, no events? (Not to mention that it's not even part of the spec).
<rant>No, it's cool, let's just keep integrating software components by one-off, non-reusable effort of reading documentation and wiring everything up manually.</rant>
Events are a portion of polymer. Unhelpfully polymer 0.5 comes up first when I google for 'polymer events' so that may have led you to believe they were deprecated.
I like that accesibility and localization are taken into account. There seem to be so frequently concerns postponed to the last stages of development...
Web component's JavaScript exists in the global scope so it can overwrite and be overwritten by scripts external to the component.
This is actually a major issue in my opinion. You can isolate your code to some extent using an IIFE but if you want to include 3rd party libraries that quickly becomes very hard to do. 3rd party libraries will also often directly modify the window object making any isolation attempts ineffective.