Portage issued the warning today on my system that 'swish-e' is going to be removed soon. However, the package chimera-bin requires swish-e. chimera-bin is in the science overlay. One solution might be to put swish-e into the science overlay too.
From the ChangeLog 15 Sep 2014; Justin Lecher <jlec@gentoo.org> -chimera-bin-1.6.2.ebuild, -chimera-bin-1.8.ebuild, -chimera-bin-1.8.1.ebuild, chimera-bin-1.9.ebuild: Drop www-apps/py-swish-e dep as it is masked