If you see that virtual/x11 is masked, this is because it's time to move to modular xorg. Modular xorg has been in the tree for quite a while now, and the long-term plan to migrage gentoo away from non-modular xorg has now been moved to the next step.
You can read how to do exactly this here: http://xrl.us/kjcy -- gentoo-user@gentoo.org mailing list
