Lots of great info. I like the basic idea of js Polymer with the binding to attributes in custom elements, this should also contribute to better performance. Haven’t looked into Polymer 2, but for 1 the code base maybe got too complicated.
For proof of concept I made a basic system in Dart https://plus.google.com/107000933666500131665/posts/MsNtp96aKwK
Some takeaways from this work. A stronger tool than js, like Dart ( or maybe Typescript) can assist the developer a lot, when the complexity grows. To build even a simple app, plain data binding isn’t sufficient, very soon comes need for two-way binding, listener binding, binding to literals and other stuff. So a design task is to define and confine a basic sufficient core of functionality.