I work in UX and I always wonder what the 'end goal' is to these UI systems... in a perfect world where every 1st and 3rd party developer on a platform builds with the same UI system, won't we eventually have every app looking nearly indistinguishable from one another? Is that really what folks want? Where is the creativity? People laughed off Apple's attempts at skeumorphism, but I predict in a few years people will be craving unique looking apps.