This bug tracks the implementation of the EAPI 3 feature mentioned in the summary.
From PMS: 10.1.15 pkg_info The pkg_info function may be called by the package manager when displaying information about an installed package. In EAPIs listed in table 10.7 as supporting pkg_info on non-installed packages, it may also be called by the package manager when displaying information about a non-installed package. In this case, ebuild authors should note that dependencies may not be installed. pkg_info must not write to the filesystem.
This is in git now: http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=06746f86b4c00ede5f7999e2e16e60f90d8f0b3a