I am not on the WHATWG / W3C, I'm just someone who implements and tracks low level JS/HTML APIs. The current direction and discussions around this topic are interesting yet seem to revolve around the concept of anonymous class instances of element definitions that ship with other elements.
The advantages of this methodology involve being able to ship completely containerized code that
is not going to suffer issues with cool-stuff
tag being registered globally when trying to
download and implement whatever-tag
which happens to ship with a competing reference to cool-stuff
.
The scoped proposal can be found here: https://github.com/WICG/webcomponents/blob/gh-pages/proposals/Scoped-Custom-Element-Registries.md