Hopefully never, and certainly not with http 2.0 around the corner (this adoption wont be so slow, things are already starting to fall neatly into place). It's

Hopefully never, and certainly not with http 2.0 around the corner (this adoption wont be so slow, things are already starting to fall neatly into place). It's a micro-optimization Google can afford to do, others will just rely on optimize images size and a CDN instead (possibly an extra hostname) and vast majority wont/don't even bother..