Honestly a lot of the stuff being added is stuff I have zero use for, and would advise people not to use because it is the same broken garbage as what CSS pre-processors do. It makes CSS more difficult to use, difficult to maintain, and difficult to work with.
But there's as much useful stuff -- and in that way the splitting the specification into "modules" as they have makes a good deal of sense. Hence why the "CSS Level 4 Selectors Module" is the only one approaching real world deployability whist much of the other modules are for all intents and purposes stillborn.
I love many of the new selectors. A good number of the CSS3 selectors moved a lot of what we had to use JS for that really should have been none of its business back into the HTML and CSS, The new "Level 4 Selectors" continue this trend with range and validity, whilst at the same time reducing even further the need for classes and ID's by giving you even more control via combinators, structural, and so forth.
On the other hand things like :scope just encourages people to ermagahd aherpaderp the STYLE tag into their BODY where it has zero blasted business ever being in the first place! Seriously, I truly believe the STYLE tag should be deprecated! Seriously it has no reason to even exist, and anyone telling you to use it probably doesn't understand enough HTML, CSS, or networking to be flapping their trap on the subject... I don't care if even Google Pagespeed is telling you to do it, it's stupid for so many reasons!
But every one of the modules is a mixed bag like that, following in HTML 5's footsteps of both offering improvements, but in many ways also flipping the bird at good practices, separation of presentation from content, accessibility, and even the intent/reason HTML exists and why CSS is separate from it. Again reeking more of HTML 3.2 / mid '90's browser wars mentality than it does anything to do with trying to make the creation of websites simpler and easier, or making the results more accessible to everyone.
Could be worse though, could be the nightmare of XML trash that is currently being labeled by some as HTML 6, dragging us even further down the road of "just slop more code in there any-old-way, who gives a flying purple fish about accessibility or logical document structure much less making things simpler/easier/better".
One step forward, two steps back.
But that's like the idiocy of CSS preprocessors which IMHO serve zero legitimate purpose if you understand even the most basic concepts of what HTML is, what CSS is, what they are for, and how to use them properly. They create an illusion of "ease" whilst making people work harder, not smarter.
With most of what they do, and indeed much of what is worming its way into certain Level 4 modules, adds nothing of value to the web development process.
Pre-processors, front end frameworks, visual editing -- all half-assed nonsense that cannot die out soon enough for my tastes. At best they thrive in a world of ignorance, at worst they are outright predatory scams! They actively encourage bad practices and methodologies better off left in the 1990's. You want to write your website that way you might as well go back to writing HTML 3.2 with tables for layout and presentational tags/attributes, pretending HTML 4 Strict and CSS never even existed.
That's how backwards what such so-called "shortcuts" are in mindset and methodology.