Hate to be the party pooper, but this to me just sounds like an easy way to monopolise on the phone industry. Just think about it, anyone who gets one wouldn't get a new phone, because they can just upgrade theirs. The company(s) making the 'blocks' can sell them for ridiculously high prices, because without them the phone is useless (or outdated). If they just sell the blocks for less than the price of another phone, people will buy the blocks instead of a new phone. Over the course of a few years, they will have to buy a few blocks for upgrades and replacements. Overall you would have paid a lot more than if you just bought a new phone, which has all the upgrades and replacements already.
Still, it would be great to see something like this. I wouldn't be surprised if it spreads to other devices as well (Laptops, computers, TVs).
Ninja: Device companies usually make things un-repairable just so you have to buy a whole new one. If you send a device to get repaired by the company who own it, if the repairs are cheaper than a new device, they could (but probably wouldn't, depending on warranties and other stuff) just tell you they cant repair it.