This doesn't really fix much - if the idea is to continue to use pixel-based positioning. I've got devices with a range of dot-pitches (surface 4 pro, external older monitor, cellphone) - with various physical screen sizes -- A "150px sidebar" doesn't work the same across these devices - and more importantly, for a low-resolution 24" screen I'd probably want a similar 3" side-bar as for a "retina"-resolution 24" screen?

But at least we seem to be moving forward from the abuse of [ed:float]-layouts for grid-systems...