We built Stencil for a selfish reason: we needed more mobile web performance for Ionic apps being deployed as PWAs (in addition to App Store apps) and we were struggling getting that with traditional framework component/bundle approaches.
We realized web components were a way forward and would let us reach more of the web dev community that wasn't just using Angular. However, we felt like there were some big framework features missing from vanilla custom elements (vdom, react fiber style rendering queue, etc), so we built stencil to make it easy to generate web components with these features baked in.
Along the way we figured other teams would benefit and pulled it out into its own project.
Stencil will be used in the next version of Ionic so we are dog fooding this hard, and web components it generated will be in use by thousands of Ionic devs soon.
We just announced this at the Polymer Summit in Copenhagen this morning and the talk is up if you're interested: https://youtu.be/UfD-k7aHkQE
Happy to answer any questions!