Sounds cool, all for it. I also have Polymer UI experience, and I have to say Polymer + Typescript makes UI development pretty fast and easy. Data binding, code error checking, and three.js is a lot simpler to use with typing information
If we do integrate, the slicer will stay TypeScript (loosey-goosey typing in JS is madness!) though the resulting Javascript artifacts should work just fine no matter how you want to use them.
So what I could do is split out a library containing just the current slicer code and other dependencies.