I saw on a year old topic that someone asked for retina support but I guess it didn't come to a sollution.
I have a responsive theme where I set my featured image to expand 100% the container is in on resolutions smaller than 480px( since they are still a lot of mid end/lower end devices with that resolution I wouldn't ignore them) but my thumbnail is 200px/200px and bringing it to almost 480px means a lot of blurriness. I was pretty happy to discover your plugin but I'm dreaming also to serve retina images to never devices with hi res screens.
Did you found something about adding the retina support or if not could you take a look at this plugin( http://wordpress.org/support/plugin/simple-wp-retina )? It serves the retina stuff server side and if isn't of much help for you I'd be pretty happy to know if I can make a mix, to use them both without any issue.