Polymer also has a lot of negatives - it still only publishes on bower for example, and the whole vulcanizing situation is sort of bleh. It also uses HTML imports for its components, which is unnatural and sort of munges concerns with the whole ES module import system - this includes importing HTML files for more traditional things such as XHR.

To me, all these things put Polymer far behind the curve as something I'm interested in ever adopting.