The porting of KDE software from Qt4 to Qt5 is in full progress. The KDE core libraries were splitted to multiple manageable frameworks, ready to be used with any Qt5 application.
On top of these frameworks (collectively called KF5 or KDE Frameworks version 5), the KDE community also ported the desktop shell and released Plasma 5.
But KDE software does not stop at the desktop shell. We have many other applications, games, and utilities, that are released either independently, or collectively with the triannual KDE Applications release.
You can find an overview of the porting status of many KDE projects at http://developer.kde.org/~cfeck/portingstatus.html (updated as time permits).
If you want to join in and help, this is a good opportunity to get in contact with the KDE community.