What do you need from WebKit next?
@jensimmons My URLPattern polyfill seems quite popular due to iOS not supporting it yet, so that would be nice to add support for:
https://www.npmjs.com/package/urlpattern-polyfill 
urlpattern-polyfill
Polyfill for the URLPattern API. Latest version: 10.0.0, last published: 14 days ago. Start using urlpattern-polyfill in your project by running `npm i urlpattern-polyfill`. There are 82 other projects in the npm registry using urlpattern-polyfill.
npm