Current fix is insufficient to really use pointer events as they are meant. Essential properties such as pointerType and pointerId are still not forwarded. Chorded button presses are not present. Pressure is not present. etc.
Also, you do not take into account and normalize the MS-prefixed event names available in IE10. The events themselves also require further normalization on several properties, because IE10 was built against an older version of the spec proposal. E.g. in IE10 the pointerType is still an integral number instead of a string constant.
If you're going to integrate support & normalization for pointer events, either tackle it completely or don't tackle it at all and leave support to a plugin.
Infact; given the fact that a polyfill is going to be desirable to support both legacy browsers and browsers from parties that are holding off on implementing pointer events (i.e. Apple Safari), maybe you should leave support out of core altogether and make pointer-event support its own thing completely.
Also, I feel that building such a polyfill plugin as a simple adapter around and on top of Polymer is a bad idea. While re-using existing working solutions is in general a good idea, Polymer adds far too much weight for old browser support to be viable in the general case.