Word is that sometime in the near future, your little avatar will be able to unlock clothing similar to achievements in the various games you play. Whether older games will be able to implement this, or only new games was not made clear.
The question remains, after you find the one outfit you like, what use do you have for new outfits? It’s probably more of a simple addition that’s simply meant to entertain and provide more possibilities to gaming companies. Personally, I’ll stick to achievement points.