One of my favorite project that failed miserably even before launching was Google’s Project Ara.

The Idea was simple and beautiful. You have phone frame and just add or upgrade the components as needed. Someone who likes to have better camera can simply add the better camera module and phone would work with the module seamlessly.
But the idea was born in 2012, and the market was demanding for better phones than the modular phones. I am guessing the introduction of the Project Ara was way too early for cellphone industry.