The newest net-im/kadu requires qxmpp library >=0.8.3, Qt5 version (at least I have not tried to build Qt5 kadu app with Qt4 qxmpp). For best flexibility, perhaps parallel installation of Qt4 and Qt5 version would be needed (achieved either via USE q4 qt5 flags or multi-slot, with .pc file and .so renames in either way).
And if parallel Q4+Qt5 support is too problematic (due to mentioned .pc and .so renames needed), at least USE flag based switch between those should be provided.
I took a liberty to add 0.9.3 ebuild with qt4/qt5 selection (no parallel installation), tests and EAPI6 support.