And with Androids, you already can download new interface packages, they are called Launchers. I use Nova Launcher, it is free, and it rocks my socks off. I can change everything down to the icons. If you want to change the notification bar, they have those apps too. This is why I love Android over iPhone, customization. And also why I am sad when I see someone with a Galaxy S3 that still has all the default settings on it.
That's a feature-fight I'd like to see Google, Microsoft and Apple get into.
Apple would never do this, customization means fragmentation. Suddenly their walled garden is editable by their end users? No no, that would be impossible.
Anyway, I feel like I am ranting now, I will stop.