This feature excites me more than any other I've seen in recent years. It allows each module to essentially "style itself" overriding unwanted cascading/inherited styles. Its a great flexibility that should have been there from the beginning.
Consider this, when it comes to the current state of inline styling, you can't put a selector into html attributes. For example, you can't do this:
This is <span>red</span>.
The style attribute only has scope to effect properties of the div, you cannot insert selectors into the style attribute to control the entire scope (of all sub elements with that div).
Instead, you must "id" or "class" the div, and use some style sheet completely outside the location of this element
to style it. This make modules too tightly coupled with the pages they appear on.
With style scopes, however, you could potentially showcase, on a single web page, a bunch of independently styled modules, without those modules having to cooperate with style-sheets of the page they are appearing on.
To achieve this now, without style scopes, it is always a pain the ass. You either have to style each attribute of each sub element (within a scope hierarchy), or play the id/class game, basically making your module have to "register" its styles OUTSIDE of itself
with the page it is appearing on.
I say, let the modules style themselves, within the module, using selectors, in the scope where they exist. Then, if you put that module on a page, its layout and look, will be exactly like you designed it to be, without having to cooperate with the page it appears on.
Additionally, I also think <style scoped> should not be limited to inline selectors, it should also have the ability to call any stylesheet URL. Something like this:
<style scoped href="AnyStyleSheetInTheWorld.css" type="text/css">
<!--Add additional styles here if necessary -->
The web will have truly matured when such flexibilities are ubiquitous. Let the modules layout and style themselves (inside themselves)!