Maybe it's just me, but it looks to me like things have been going the other "way", all your documents synced to a "cloud" and providing various interfaces to it (phone/tablet/pc...)
What this looks like is all your data on your phone's hd, and "docking" to other form factors to compute/play with the data locally. I really hope we go this route, but I'm not holding my breath.
I don't think it's about where your documents are, I think it's more about where your local CPU is. Your documents will almost certainly be in the cloud. However then you have two radios, two CPU's, two sticks of RAM. I think the idea of convergence is merging your phone, your PC, and any other device with a CPU into one device. The data will still be in the cloud. The benefit is if you want to write something. A keyboard, and large monitor is better. If you want a phone, the smaller form factor is better. You want a better camera, you buy lenses... not a body. etc.
There's no good reason to have a separate CPU in each of these devices. When you can fit a CPU that's as powerful as a laptop in a phone, why not just have it in the phone, and only have one computer? Then take the CPU out of the laptop, and plug in your phone when you need it.
A mid-to-high end ARM SoC is $20 these days, there's really no reason to NOT have a CPU in anything that has a monitor in it. Especially since the CPU in a phone has to deal with a power/thermal profile that most laptops have a little more leeway on. It's such a false economy.
It's still kind of nice that it should become possible, with pretty much no fussing, to plug a phone into a TV (or any other display with USB input), have it charge and also take over the display.
As you say, the hardware savings aren't very interesting, but simpler, better interop looks like it will be.
ARM's big.LITTLE architecture could feasibly bridge the gap between mobile and portable devices. I recently acquired a ODroid XU and a bunch of peripherals to serve as a modular mobile computer. Right now it complements my laptop and phone, but eventually I could see it replacing both by getting a small "tablet" that's basically a display/speaker/mic and a pico projector + tiny wireless keyboard. All of these components already exist, but the LCD and projector are currently out of my price range for what's essentially a fun experiment. There are even battery banks available for around $99 that can charge USB plus many laptop models, and can be used while charging (something most cheaper USB battery packs don't do).
The biggest issue will probably be keeping the thing powered all day. In the medium term I can even see the possibility of a shift away from ultrabooks and toward more modular laptops, since the giant battery needs to live somewhere. Then you could have a mobile device tethered wirelessly that doesn't need the same level of components (except maybe GPU) and the battery can be reduced further.
there's so much more then a CPU though. You still need some storage, radios (bluetooth/wifi/4g), connections for the radios etc.
Plus, if as technology gets better you have to upgrade each device independently. Wouldn't it be nice if every two years you could upgrade your phone AND your laptop for the price of one device?
A phone uses about 5W, a laptop 50W and a ultra-high-end desktop 500W. That's two orders of magnitude of difference, no way the CPU can be the same for all that.
And then your kid wants to use the computer but can't because you have the only CPU in your phone and you kick yourself for buying into the modular convergence snake oil.
If you were buying in to modularised hardware that worked that way then instead of buying your kid a tablet, they'd have a phone-style device.
It's more like you have a phone with thermal imaging built in, and your kid wants to use thermal imaging for a homework project, so now you can't use your phone.
Whereas with modularised hardware – like appification of hardware – then you'll be able to continue to use your phone (maybe to boost the processing capabilities of your desktop whilst you do a render or plugged in to your VR headset) and hand them the thermal imaging module to use with their processing device (be that a phone, laptop, or whatever).
I think the focus is more on the fact that there is hardware and protocol which will enable data transfer at that bandwidth and speed. I completely agree that everything is going into the cloud but that is usually personlized data. What this would allow is a massive pipeline of data transfer between actual hardware. For instance,a range of hardwares like a high res camera to maybe ssds or possibly holographic data storages, etc etc.
What this looks like is all your data on your phone's hd, and "docking" to other form factors to compute/play with the data locally. I really hope we go this route, but I'm not holding my breath.