@brainblasted @sonny yep, we implemented that in elementary OS. I'd love for someone to port it over to GNOME!
The one sort of caveat to the elementary implementation is that it does it so well with the default wallpapers because it’s using explicit metadata stored in the image file itself, which helps paper over the color selection sometimes not doing exactly what a designer would do. Whether we also went that way for GNOME or just used a color matching algorithm, it would still be nice.