I like web components for rendering and localized state... I think it's pretty clean and works. That said, I like react over polymer for structure, and combined with Redux for control flow.
I'm the end we'll see more web components, not sure about polymer though... it really depends on the application though. React does well with crud apps with some shared state and minimal points of interaction... polymer and web components do better the more interaction needed (animation, lots of drag events and ui to go with it).
In the end it's a matter of using what you like and what makes sense... most applications shouldn't be that complex and people tend to make them more, not less so.