I just read this article about Project Ara, Google's project tasked with creating a phone platform that is customizable with different plug in modules. For example, what if you never took pictures with your phone (hard to believe, I know)? You could use that space to plug in an extra battery, or an external speaker, a card reader, a better antenna, or anything else that module manufacturers can dream up. Imagine the possibilities!
I don't believe the carriers will embrace this vision of the future - this could open up the way for you to upgrade your processor, or easily replace broken screens or input jacks. If you could easily do this yourself, why would you pay for phone insurance, or upgrade to a new phone every two years - you could conceivably add new features to your phone whenever you wanted to.
Apparently, the base kit (without screens or any other modules) is scheduled to go on sale next year for $50. At that price, it's definitely worth a look.
More information on Project Ara: