Hmmm… Some of you may like this.
Bespin developer Thomas Luebking's new creation for Qt5, Virtuality:
https://aur.archlinux.org/packages/virtuality-qt5-git/https://aur.archlinux.org/packages/virtuality-qt4-git/Seems the Qt5 config utility affects Qt4 apps as well though you need to install Qt4 one too to set the virtuality theme for Qt4 apps.
Virtuality has already three subsets/presets (flynn, sienar, virtualbreeze) though they're just some minor hardcoded color sets in very few areas which you can achieve via virtuality's control panel anyway.
As always, you need to add one of these to your ~/.bashrc (and then relogin):
export QT_STYLE_OVERRIDE=virtuality
export QT_STYLE_OVERRIDE=flynn
export QT_STYLE_OVERRIDE=sienar
export QT_STYLE_OVERRIDE=virtualbreeze
Theme/widget style itself is too experimental or modern for me; hopefully it quickly gains the vast configuration options of the late Bespin.
Changed colours aren't honoured by Qt5 apps and this issue has already been reported in github (I'll participate after this as well).
There's also the new version of quantumstyle (a different qt engine by a different dev):
https://aur.archlinux.org/packages/kdestyle-qsvgstyle-kde4/Don't pay attention to "ked" parts in the above aur naming it's a qt utility as virtuality, but this one is a Qt4 app (at the moment).
It seems Qt theming requires a thread of its own.
