It seems that it should depend on dev-python/pygobject:3 and x11-libs/gtksourceview:3.0 Now it only has dev-python/pygobject:2 dependency. Without dev-python/pygobject:3 it failes to start with "ERROR: PyChess requires pygobject to be installed." With explicitly installed ev-python/pygobject:3 it fails with "ImportError: /usr/lib64/python2.7/site-packages/gi/_gi.so: undefined symbol: _Py_ZeroStruct" With explicitly installed x11-libs/gtksourceview:3.0 it starts smoothly.
should be better now. thanks for the bug report.