Nothing finished yet, performance issues (because guess what, polymer's routing turned out to be pretty much the same as a 'tab panel'), aaand Polymer 2 rolls around, backwards incompatible. Scramble to make all their components suitable for Polymer 2, and they're just about to sigh a breath of relief aaaaand polymer 3 rolls around and becomes deprecated in favor of lit-html at the same time.
Moral of the story: Ex-Google doesn't mean shit, and don't force the use of experimental technology for your whole fucking multi-billion company.
They should've stuck with Angular, it's fine, or migrate to React instead which has / is becoming an industry standard.