[oops]

The Stripe gallery posted here the other day[1] used src-less img tags for lazy loading. It looks like they handle the script issue by having the normal img tag (with src attribute) nearby in a noscript block.

Doesn't really do much to help with the overhead of modifying existing markup. Perhaps if you're already using something like image_tag in Rails, a retina_image_tag helper might not be too much of a stretch.

1: https://stripe.com/gallery