ARS Technica reports it looks like Apple is working on MacBooks with high-DPI screens. Perhaps these systems will be launched along the release of Mountain Lion.
A new clue found within in the latest developer release of OS X 10.8 (Mountain Lion) suggests that 2012 may bring us the "summer of retina display Macs." A source with access to the latest Mountain Lion preview alerted Ars that double-sized graphics have popped up in some unexpected places, once again suggesting that Apple may be close to releasing MacBooks with high pixel-density screens.
One example comes from Messages, Apple's replacement for iChat. While using the app under the second developer preview of Mountain Lion, some icons are erroneously displaying 2x resolution art. In the image below, the "audio chat" icon is a 2x version instead of the standard 1x version, according to our source.