This is mainly for fixes, workarounds, or development/testing (and quite a few LTO hacks of different kinds). New-ish stuff includes dev-ada/ updates to use system-gcc instead of gnat-gpl (requires ada-overlay to get Ada language support via USE=ada).
The master branch is intended to contain working (as in buildable) ebuilds, while unfinished or otherwise non-working ebuilds are now on the wip branch (not shown below).
You can (optionally) add this overlay with layman:
$ layman -f -a nerdboy -o https://raw.github.com/sarnold/portage-overlay/master/configs/layman.xml
Latest (sort of)
Other than Ada tools for that shiny new FOSS compiler (and more LTO fixes) the latest new-ish "thing" are the iMX etnaviv drivers, plus DRM support and the xf86-video-armada drivers. Yay for FOSS GPU acceleration and an actual X desktop on most iMX6 machines (eg, wandboard, udoo, nitrogen6x, and cubox). Most of the new ARM goodies are in the Gentoo ARM overlay.
Also, check out the new Gentoo wiki page for the amr64 espressobin board.