When I think about what front-end development really is and feels like, this is at the heart of it: designing around a huge set of unknowns, and really embracing that notion as a strength of the web rather than a weakness or unfortunate truth we have to work around.
Cathy Dutton digs into this with real code and examples over on A List Apart. A recurring theme is the idea that content (certainly an unknown, since content changes) can and should drive design decisions. It is even floated that container queries might not be all they are cracked up to be since they are still based on a parent, not content.
It’s hard to say for sure whether container queries will be a success story until we have solid cross-browser support for them. Responsive component libraries would definitely evolve how we design and would improve the possibilities for reuse and design at scale. But maybe we will always need to adjust these components to suit our content.
We can’t design the same way we have for this ever-changing landscape, but we can design for content. By putting content first and allowing that content to adapt to whatever space surrounds it, we can create more robust, flexible designs that increase the longevity of our products.