As much as I hate it, I think you (we) are in the minority here.

Given how many geeks want better battery life over shaving a few mm off a device, and how that is exactly the opposite of what is happening, I think it's fair to say that the broader market want a slim phone.

I've not seen the dimensions of the prototypes yet, how bulky are they actually?

There is an interesting anti-slim trend on the outskirts of mainstream smartphone news; ruggedized phones like the Caterpillar S50 and Runbo X6 are three times thicker than fragile 'stylish' phones and would seem good candidates for Ara. Often it is internal components that fail.

In a traditional phone that should not break at all you can simply solder and glue everything together so that things will simply not break; then you put it in a casing that is water/dust/shockproof and be done with it. I guess ensuring the same thing for a modular frame might be harder. Drop it and get a slightly bent internal frame so that the screen module can't connect anymore, etc.