The feature freeze for R 2.7.0 is in place with an expected April 22nd release. I've noticed some of the locale stuff has changed recently (LC_CTYPE and the like) so I'll need to fix those warning messages. Right now I'm setting up the IKImageBrowserView-backed graphics device interface for the GUI, though the built-in quartz device has been serving me well so far. There are a couple of reasons for the view set up, which uses bitmaps to represent the graphics device on the backend. After the page is completed, the bitmap is converted to a more efficient representation (e.g. PNG) for temporary storage and the display list recorded into the device. We'll also continue to cheat and provide a Cover Flow mode (no, I don't care that it's a private API).
Another interesting feature is that, unlike the current Mac GUI, the graphics device is considered a View on the same Model (the interpreter). We'll see how it plays out, but that might help with some of the fancy footwork usually required when dealing with the NSDocumentController.