Honestly, I need to support retina screens for mobile and desktop. For non-retina screens getting a larger image doesn't really matter. Non retina mobile devices are rapidly disappearing. So therefore I'm comfortable delivering higher resolution images to all devices.
I optimize our images by making them as small as possible and using lazy loading. These two techniques are more than adequate to suit out needs right now.
I am (loosely) of the opinion right now that this is an answer in search of a problem.
An example I just tried was 38kb at 1x and 105kb at 2x
Must be nice to only have big-city first-worlders as users :)
Unless something's changed since the last time I looked, media queries are only screenwise so they don't gracefully handle having a block in a small sidebar versus a "central" content section. The sidebar images could actually grow from a big to a small screen (because content is linearised and the "sidebar image" now takes the whole width of a small display, rather than a small part of a big display)
Pictures are they only problem that needs to be solved at this point.