I must be the odd man out in this conversation but I like the whole concept of modularity: Heathkits were cool. Separates in the audio industry was even better. I helped rebuild a VW dune buggy and learned immensely from the process. Building your own computer from components/hw was satisfying. Gamers created a whole cottage industry and benefits of high end computer parts are still with us but almost on its last leg. Even Arduino lovers can't be wrong. Along the same lines, instead of the current throw-away smartphones that fill entire dumps, being able to upgrade incrementally, a la Project Ara, sounds nice but something tells me it will not get to a maturation state. And too bad for that!
Another question to ask is "why would a vendor put the effort into creating a module for Ara?" or rather "who will be making these modules?"
A vendor can sell a camera to many many product creators. However, if the vendor creates a camera module for Ara, it can only be used on the Ara market. Is google to going to make these extra modules? They're the only ones with incentive.
Junko, it is a bit odd that Google has focused this solely toward smartphones. When you factor in certifications and software compatibility, this just isn't a viable solution for a usable smartphone. However, I would agree that it does make an innovative development platform for IoT and embedded applications.