But! After three years of debate, a few new pieces of markup have emerged to solve the responsive images problem:
and our old friend source (borrowed from audio and video)
I predict his won’t gain good adoption, the true solution here is to make a new image file format that bundles the sizes and sends only the correct amount of bits needed. All other predicted solutions of this to date but too much of the onus on the web developer and designer. This is a problem that can be solved by the dev tools and server, not the fallible people building the sites.