Many responsive image techniques require modifying img tags with additional data attributes, see here:
http://css-tricks.com/which-responsive-images-solution-should-you-use/
Also this is a good resource for responsive stuff:
http://mashable.com/2013/03/18/web-design-tools/
Would be great if there was a server setting where we could globally modify images based on some sort of convention. Alternatively or in addition to, integration with something like Matt's Adaptive images http://adaptive-images.com/ could work as well. However it would require that LR comes bundled all with high res images and relies on AI to scale them accordingly.... this of course also assumes we can find a workaround for it serving up images related to containers and device size, not just sending device width images along.
