As mentionned here https://github.com/KDE/akonadi/commit/9c0dc6b3f0826d32eac310b2e7ecd858ca3df681 there was a known bug in Akonadi 1.13.0 that caused Akonadi to not clean up old data files. At the moment, 64GB additional disk space is taken on my system. Is it possible to include the patch in the ebuild? Thanks.
That might be a good reason to move akonadi-server-1.13.1_pre20160203-r1 into tree - it is available for testing in kde overlay.
Thanks, Andreas' snapshot (which contains that patch) moved to main tree. https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=086d38b7bccc6890437cf096ba0440f968584ea6