Username or EmailPassword
I do agree. What you are speaking of is easily one of the best things about KDE. From a develoment perspective KDE is easier to create applications with. That is what gnome was trying to do with Bonobo but... oh well.
But the problem is that those ideas need to come out in the user interface as well. I would be floored if KDE came out with a more simplistic interface but with the ability to insert system wide pluggins/components.
Look at what the model has done for firefox. Firefox starts out very simple. But I can add web development tools, ad blocking, tab customizations, I can even add audio controls. Now think of that on a large scale.