Pantheon

Pantheon is a new lightweight, modular desktop environment primarily written in Vala and GTK+, for the elementary OS project.

Installation
Pantheon currently resides in the elementary overlay. You will first need to ensure you have layman installed. Then you will need to add the elementary overlay.

Next, we need to add the ~arch keyword to allow installation. At the time of writing only ~amd64 is supported. After keywording pantheon-base/pantheon, portage will give instructions for all dependent packages that also require a keyword. A list of required keyword changes is supplied below.

You should ensure that X is included in your global USE flags. Beyond that, I've added a list of other necessary USE flags to install pantheon.

There were also a few packages that were hard-masked in portage. These will need to be unmasked for now:

Next, I encountered a blocking package between vte and gtk+. I started by emerging gtk+ first: