It has to work in all environments, not in KDE only. And dragging all kinds of KDE stuff in would make sure that it doesn’t work outside of KDE any more. Even if we assumed that all GNOME users use the YaST Gtk UI (which is not the case), there are also Xfce users, BlackBox users, WindowMaker users, AfterStep users, FVWM2 users, you name it.

We made a conscious decision not to feel all those people left out by telling them “if you want YaST, you’ll have to use the NCurses (text-based) front-end”.

So it’s plain Qt, not KDE. And as a Qt application, it is integrated into KDE like any other Qt application. It uses the widget style and widget colors set in the Qt defaults. You can change them with /usr/bin/qtconfig (for the YaST modules) and with /usr/lib/qt3/bin/qtconfig (for the YaST control center which is still a Qt3 application).

It’s the job of the KDE control center modules to export values changed there properly to those Qt config files so the KDE widget style and colors is used in Qt applications, too.

As for trying to pretend YaST modules were KCM modules:

We had that for a long time (in parallel to stand-alone YaST modules), and it was a royal disaster. There were minor issues like keyboard focus that just didn’t work sometimes (without any way to recover).

And there were design issues, too: Most YaST modules are wizard-like. They have a workflow with multiple steps and [Prev] [Next] buttons. This just doesn’t work out with the model of KCM modules that are intended to be one page (possibly with multiple tabs) of settings. Not only does a wizard look way out of place there, it’s also poor usability to try to press it into the KCM model.

And BTW like that other reply said this is all way off topic.

For example, why doesn’t Yast obey whatever you’ve set the widget style to be? Or for that matter: why aren’t the different modules implemented as kcm-modules? The first may not be as important, but personally I would love to have to have the different YaST modules incorporated into KDE’s system settings instead of in a specific tool. Or if that’s not feasible for some reason: make it feel like a KDE app instead of “just” a Qt one. Yes, it was not written with KDE specifically in mind but somehow I do think it’s just the KDE4 users that uses the Qt front-end so why not go all the way?

Note: I know the Qt4 frontend is quite new so if stuff like what I outlined above is planned for the future, my apologies. I just feel it would make the whole installed system more coherent. And I love yast otherwise, so take it for what it’s worth: a few pet peeves of mine. I just like my system(s) to be consistent and every setting available from one place.