A previous solution based on explicit naming of "parts" of shadow DOMs was withdrawn several months ago. And update was given the the CSS WG last November that outlined the changes. FWIW, the "::part()" solution would have _worked_. It's entirely feasible that we could have improved the world by providing Shadow DOM with that as the primary styling mechanism. Not ideal, though. So we have been willing to change course in response to feedback.

Here's the Blink bug: https://code.google.com/p/chromium/issues/detail?id=309504

All of this happened in the open, in consultation with other vendors (not necessarily at WG meetings, which aren't where you design features anyway).

Remember the context here: Googlers have been doing the heavy lifting on this front for _years_. It's exciting that others are starting to pay attention to the problem space. That they don't think providing Shadow DOM to users is as urgent as we do is their right. We, however, are willing to take some pain in this (relatively small) instance, should they not be willing to help us work through the naming issue in short-order (which, as you can see from the thread, is the actual request; our goal is to improve things through web developers, preferably via collaboration.