We had a recent very, very long forum discussion about this actually:
Basically you can increase your font sizes in the Appearance preferences and most things should be scaled up. Unfortunately Tracker and Deskbar have to be restarted to get the new font sizes. You can hold Ctrl-Alt-Del to get the Team Monitor which has an option to restart the desktop (which means Tracker and Deskbar.)
Let us know how this works on a Retina screen and maybe give your opinion in the above thread. I posted something recently there about how Apple does the scaling in macOS which is not that great.