First thing that came into mind when I heard about project Ara was that, laptops aren't modular because the increased size and weight will out weigh the benefits. Seemed like the same situation applies to smartphones, only worse.
Now we have come somewhat full circle with Apple's Macbook which has meagre hardware functionality and relies on USB-C to provide the missing functionality in a modular fashion. However it means a nest of cables so it's probably not what anyone wants when they want a modular laptop.
We didn't have to go down the road to soldering all the bits to a tiny motherboard, but Apple's vision of "small and light at all costs", including performance and battery life, killed all the other paths for the foreseeable future.
I might investigate EOMA68 stuff, though it is likely years before it'll be viable, if ever (especially given their anti-intel sentiment): http://elinux.org/Embedded_Open_Modular_Architecture/EOMA-68
Apple is the only vendor that has a 15" laptop with high-res screen and quad-core processor that gets 8+ hours of battery life. The only laptops with greater battery capacity than the Macbook Pros are the Thinkpads with extended batteries that stick out of the machine.
The PC was the outlier that allowed for easy expansion.
Now we have USB instead of Amiga expansion bays, that required a table with big enough width. Instead we scatter cables and hubs.
People forget Apple was sued, and lost, in the 1990s for telling people to buy new iPods instead of selling replacement batteries. They started moving to user serviceable stuff briefly, but then went back to their own ways and people haven't challenged them since.
https://en.wikipedia.org/wiki/Apple_Inc._litigation#iPod_bat...
It was the 2000s, 2005 was the settlement date, iPods didn't exist in the 1990s. They didn't lose, strictly speaking, they settled (which is not the same as admitting fault). Settling lets them save face, even if they may not have had a liability, by not dragging their name through the muck with regards to the poor performance of the batteries and iPods.
The battery is swappable, and the whole thing opens with a set of phillips (you know, the '+' shape) screws.
Although you can't choose the GPU when ordering, newer ones tend to have newer models, implying that's also modular (just fixed to a selection of one at a given time).
So, yeah --- you can get a modular laptop, but you have to know where to look.
And how much did it weigh? Laptops have come a long way since even just 10 years ago. My rMBP is almost a pound lighter than my original Macbook, despite having a 15.4" versus 13.3" screen, a quad core versus dual-core processor, and a 96 watt-hour battery versus a 55 watt-hour battery.
And even if I was willing to cart around that extra 0.8 pounds, I wouldn't want to spend that extra weight budget on increased modularity. I'd much rather they, say, push the battery life to 14-15 hours instead.
There's no point adding any extra module, people do not upgrade anything besides RAM, and everything that wears off is included.
PCMCIA was so great. In my entire experience of computing and consumer electronics, I think PCMCIA is still my favorite technology. I miss it a lot.
It _would_ add a little size/mass overhead, but it wouldn't have to add a lot. It would just cut in to bottom lines to build and maintain a consistent form factor. Allowing people to replace parts means they'll be buying fewer new units. My last two laptop purchases were definitely due to a hypothetically fixable problem in an unrepairable form factor.
Making the screen completely modular would be one way to achieve this, since you can just replace the screen with a new one if the old one breaks in a drop. But it can be achieved much more easily and cheaply by simply slightly recessing the screen (or by slightly raising everything around the screen) so the glass never has to make direct contact with concrete in the event of a drop.
This is how bumper cases work, and my $3 bumper case has saved my $400 phone enough times that I'd never use a new phone without one. That said, I really wish this kind of resilience was built into the phone itself, so I'd never have to have to cover up the nice design and great feeling materials on my phone with a cheap, bulky, hideous case.
iPhone 4/4S did this just fine, undo two screws and the glass comes right off ready to be replaced for like $10.
iPhone 5> they started fusing the glass to the sensor IIRC so this became far more expensive/cumbersome
I've had good luck in choosing phones with cases just elastic enough to break a bit while protecting the screen (even without any kind of cover). But I never brought into the hard-case movement by Apple.
That's not what sales numbers say. People repeatedly buy the thinner/lighter models (which also seem more "advanced to then") over heavier alternatives.
Focus most of your efforts putting the good stuff into the thin phones and then run the numbers how everyone is buying thin phones!
I think those are quite different: a phone that screws/clips together where you can replace a damaged screen is a very different prospect from one made of pluggable blocks.