QKdeTheme constructor is private

Currently, the QKdeTheme platform theme class has a private constructor, disallowing deriving from this class. Each object is created by a special factory, QKdeTheme::createKdeTheme(). The factory method determines automatically the required parameters (from the environment) to the constructor and returns a new object.

There seems to be no real reason for the constructor to be private. Sometimes, when writing custom platform themes, to conserve the look-and-feel of a given desktop it is useful to be able to derive from an existing KDE theme. Because the constructor is private, it is not possible to enhance existing functionality, the only way being to re-do existing work already performed by Qt5 developers.

If there is a reason for making the constructor private, please comment. The risk of allocating a QKdeTheme object bypassing the factory seems to be close to 0.
Making the constructor public would be helpful. While keeping it private seems to not give any obvious + at all.