From The Register.
"A modular phone that will let you snap on and pull off different components as you wish will finally launch this fall, Google has announced."
Sounds like a solution looking for a problem to me, based on the video. How many people want to change their phones hardware many times a day?
In theory the occasional module upgrade to improve the phone would be good, say adding a newer camera, faster CPU, etc, but at what cost? Probably lower reliability, potential compatibility issues, probably larger size because parts have to be self contained and packaged.