I even think this is how Google would have beaten the iPhone. Android as the OS for an ever-evolving phone, where if a user needs more ram he would just add more, if he needs a new processor he would just replace the current, if he needs a higher resolution display the old just would get replaced. Of course that is not easy, of course in the beginning a tailor-made smartphone would be slicker, faster. But then you support it some time and you get loyal users upgrading their device instead of even considering something else.
I know there are limits to upgradeability, just as a PC reaches the moment where all that remains from its old incarnation is the case. But still, enabling upgrades and thus removing consumers from the market would be a huge hit to all other smartphone vendors, probably spawning a more targeted parts industry.
And no: The current module system from LG or what Ara was presenting in the end is not it. Adding a new photo lense interests no one. You need to be able to switch out the core components to make an impact. The Fairphone 2 comes close, but I don't think you can drive real core upgrades without controlling the OS, and thus it ends up with a core module. We'll see. If they manage to add things like replacing the display with a better display, the core module with a more powerful one, that might already be good enough.