It's a pity that the networks we currently use cannot be guaranteed to be secure and that there is strong emphasis on undoing decades of good work in microcomputers by shoving data to the other side of the world instead of using it locally!
Further into the future it's possible (although unlikely in my opinion) that we could use a mesh network to relay signals along series of other people's devices until it gets to a place where there's a connection to a cell tower available. The power requirements would be a problem, and there's the issue of data privacy, but it's theoretically possible.
We won't ever have a 100% coverage (with a free roaming and all that). It's impossible.
> Underground metro systems will need cell towers
You'd have to wait few more centuries for this to happen. They still can't get rid of the signalling system from the 1890s.
> Alternatively, tube trains could have their own wifi that connects users to the internet.
They can't even consistently communicate with the train drivers at the moment.
> a mesh network to relay signals along series of other people's devices
In a middle of a desert, in an open ocean, in a taiga, on a spacecraft light seconds away from the Earth?
No way. We still need to cram as much compute power into as little space as possible. All the cloud fancy stuff is nowhere near a substitution for it. And no network improvements would ever overcome the speed of light limitations on latency.
I'm sure there'll be edge cases where it won't work and we'll need other options. That's fine. It doesn't detract from the point that having a connected device that can access a cloud computing platform is exceptionally useful in 99.99% of cases. I'm not suggesting that means we can stop all mobile device innovation.
This is exactly the unfortunate attitude of most of the mobile apps developers. Exactly the reason why I can't use most of the apps, even the high profile ones like the BBC News. They must understand that it's not anywhere close to 99.99% of cases, that a good connection is available more like 10% of an active time, and, therefore, a great deal of caching and prefetching is mandatory. If most of the time most of the functionality of my mobile device is not available I'd rather stick to the tiny subset that is available consistently and ignore the rest.
And I suspect that most big cities got a similar patchy coverage pattern as in London.
However, in terms of the accessible hardware I think we already have that practically limitless supercomputing power in our hands. The paradigm shift is in the realisation that "your computer" is a device that computes things, regardless of where it computes things, rather than being the beige box in the corner. With a little code and enough cash I can access millions of CPUs and terabytes of RAM from my phone. The fact that computing power isn't actually in my phone doesn't matter in the least.
The computing revolution is the network, not the CPU.