Phonebloks was already an interesting concept, and now Motorola's getting behind it. I think it's a solid idea for the reason that I think the new Mac Pro is a solid idea: Not all components are rendered obsolete at once.
That said, it's not without problems.
- Size. Durable, modular connectors take up valuable space. If you're comfortable with a larger phone, this isn't a problem.
- Integration. The big push in mobile has been to get into System-On-A-Chip (SoC) designs, merging the CPU, RAM, and all wireless capabilities into a single chip.
- Efficiency. Again, the SoC solution fits here: You use less power when you're not "leaving" one chip to get to another function.
- Performance. See above.
Mobile's a little different from desktop in this regard, and I see a huge potential for this in low-income and underdeveloped populations. That's a huge market that's massively underserved. I don't see it selling well to a luxury market, however, and I absolutely expect this to be picked up by the tinkerer/hacker communities.
Just for some basic off-the-cuff thoughts, here's some lifecycles that I've seen for mobile components, in terms of how often they could be replaced:
- Displays - Two years. Apple went through three iPhone generations on the same display, then two more on the Retina Display, and now they're on year two for the 16:9 Retina Display.
- CPU - One to three years. Upgrading is nice, but you can realistically stretch a CPU until it's been outclassed twice before really worrying about replacements.
- RAM - Two to three years. This depends on the OS, but there's been a push to make things more efficient, not less. I suspect that this will add some life to the memory module.
- Graphics - Variable. Do you need to play games on your phone? Upgrade yearly. No? Maybe every three-four years.
- Wireless - Variable. Bluetooth can probably get by with anything from two years to indefinitely. Wifi, maybe two-three, again, depending on your own needs. I've got some devices at home still using 802.11g.
- Cellular - Ideally, every two years. Power efficiencies, speed boosts, jumps from 3G to 4G and beyond, there's definitely a few good reasons to swap out occasionally.
- Cameras - Whenever you'd like. If it's even halfway decent today and has a flash, you have to be pretty into snapshot photography to consider this a major factor.
Honestly, I'm more concerned about the system chassis than I am about the modules: As things get faster, will you be able to shuffle data to and from modules as quickly as you need? That goes to the bus/chassis design, and that's something that I would certainly leave to Motorola to solve.