Somebody dropped ~ppc from =dev-db/mysql-workbench-6.0.{7,8}.
Probably because of a new dependency: dev-db/vsqlite++
Looks like I did forget to file a bug for this. Please test and keyword: >=dev-db/vsqlite++-0.3.12 >=dev-db/mysql-workbench-6.0.8
02 Mar 2015; Agostino Sarubbo <ago@gentoo.org> mysql-workbench-6.0.9.ebuild: Stable for ppc, wrt bug #505798