I've used a similar technique on sites for many, many years .. specifically using the calc function to define body-level font sizes (page dimensions ratios) for

I've used a similar technique on sites for many, many years .. specifically using the calc function to define body-level font sizes (page dimensions ratios) for each breakpoint, which can then be used to size everything else on the page (eg. img = 16rem; margin = 2.4em). It works really well, and saves a lot of time with responsive design as you only need to consider each breakpoint / ratio change. I don't think it's a particularly novel concept though.