9to5Mac reports that Apple is in the late stages of testing new iMacs that have higher resolution displays. We could reportedly see the new Macs at an event in the next couple of weeks.
It's not clear what resolution exactly the new iMacs will have, but OS X Yosemite has references to 6400 x 3600, 5760×3240, and 4096×2304 displays. There's also reportedly new versions of Final Cut Pro and iMovie support new higher resolutions. [9to5Mac]