When and if WebKit implements Shadow DOM, we won't use these vestiges of the old code. Note that this checkin (and the earlier actual removal of the old implementation) are not a commentary on our long-term plans to support it or not.
The checkin message is a series of inside jokes, which I see have confused many people. You can just interpret this as "remove some remnants of dead code, also I am a bit of a jokester". (Where "I" is the author of the patch, not me.)
Specifically, the references to 60fps, mobile, and 8.8 million lines are all jokes. I hate to explain jokes. But I see a lot of people in the comments trying to read serious deep meaning into these that is just not there.
I don't know if I got it wrong, but for me, as soon as I read it, it was an obvious joke reference to Google's BS excuses for removing Adobe's CSS layout code from Blink.
They used the same speed, mobile and "too many lines of code" comment, IIRC.
Also, knowing that Google really pushes and wants the Shadow DOM (see recent hoopla with W3C about them shipping their own version ahead of standard), WebKit removing it could also be seen as a FU to Google.
Inside jokes are good fun at the time. The problem is when you come back to them later and no longer remember the context. I can just imagine a manager coming in a few years' time and drawing a wrong conclusion from those lines and using it as the basis for doing something that dooms the entire company. (Somehow.)
Change "million" to "zillion" and put the words and phrases "synergy", "looking forwards" and "value-add" and no developer would ever have guessed that it was anything other than a joke.
I don't check in to WebKit as much as I used to but I probably would not choose to make my own commit messages quite so inside jokey. That being said, we try to have fun on this project.
Many WebKit developers are very actively commenting on the Web Components family of specs. We don't generally comment specifically on future implementation plans though.
The checkin message is a series of inside jokes, which I see have confused many people. You can just interpret this as "remove some remnants of dead code, also I am a bit of a jokester". (Where "I" is the author of the patch, not me.)