Since version 7.4 of our theme we have added retina support for featured images. This functionality is available for all themes thumbs including smart lists, modules and blocks post featured images, galleries and was developed based on the recent WordPress 4.4 native responsive image support addition.
To enable the retina support go to Theme’s Panel > Block Settings and expand the Thumbs on Modules/Blocks section. You find a retina switch for each image thumb size. Retina thumb sizes are disabled by default so you will have to enable the retina support for the image thumbs you use then make sure that you regenerate thumbnails.