I would love to see this take off, but I worry that everybody thinking about it has the wrong idea about modularity.
Tweakers fuck with their phones on a daily basis. They'll jailbreak, load new OSes, try out a dozen apps a week and own two or three cases. I'm not going to pull numbers out of my ass, but my experience holds that these guys ('cuz they're never girls) are a minority in the market.
Yet these are the guys that are focusing on "modular" and they're designing it around themselves - thus the magnets to hold shit together, thus the oversized chassis, thus the "tweak on/tweak off" approach to design.
Me? I'd tell AT&T, Verizon, T-Mobile, Claire's, Best Buy, Ben Bridge, Nordstrom, you name it that I'm selling franchises for a line of phones that follow the "watch" model. I'd sell tool kits and certification for cost and I'd put certified techs on my website and allow them to advertise for free. Then I'd come out with a chassis that doesn't go together like legos, but can be upgraded in fifteen minutes by a semi-skilled technician with a satchel full of tools.
Most people are going to want to build a phone that does what they want and use it. If it doesn't do what they want they'll want to swap maybe one or two things, not everything. The majority of the design is going to be static - yes, you'll want to be able to take it apart but you aren't going to be doing it at parties.
Even then, you could build a "sled" chassis that allows you to hardpoint on removable components. You could use it for prototyping, you could use it for demoing, and your geeks could rawk it all day long and swap modules in and out like legos. 'cuz really:
A photographer is gonna want lenses. He might swap from a video CMOS to a still CMOS but he's more likely to have both installed.
A health nut is going to want bluetooth and possible pulse ox. He's good with everything else.
A fashion maven is going to want a half-dozen easy cases.
Everyone is going to want a couple batteries.
Other than that, shit's gonna stay put, mostly - the chip will stay until it's old. The screen will stay until it's old. The keyboard? Yeah, people might want a keyboard they can put on and take off. But most of the modularity of the design doesn't really need to be user-operable and that seems to be the model everyone pursues.
Were I Google I'd build a big goddamn ecosystem of module prototypes, open-source them, then get my "explorer" program in gear to get hardware devs and an ecosystem of bodega repair and upgrade shops. And then fuck apple.
I'm not Google though.