The solution would be to create separate packages for plugins. KWallet support would be activated by installing qupzilla-plugin-kwallet.
I believe the hard dependency on KDE is a big mistake and even goes
against the wish of the author. Even as QupZilla/Falkon is becoming a
KDE project, it is mentioned explicitly that "there will be no hard
dependencies on KDE libraries"
(http://blog.qupzilla.com/2017/08/qupzilla-is-moving-under-kde-and.html).
QupZilla is meant to be as lightweight as possible and pulling all
those KDE dependencies is just awful.
