Ubuntu on a tablet is a bad example. You're running a PC OS on a tablet. For 99.9999% of users mobile = iOS or Android.
I'm talking about platform here, not just hardware. I could run Ubuntu on an old Samsung Galaxy and hack a way to connect it to a monitor, but then it would be a PC in a small box not a "mobile device."
"Old people said the same about the command line, it was never going to be replaced for real work."
They were right.
Leave "old" out of it. When I was a teenager I was a Linux head. I remember my dad telling me that stuff was stupid, since GUIs were going to replace everything. I told him (then about 40) that you'd never replace a command line with a GUI for all kinds of tasks. I was absolutely right. It's 2014 and you still can barely script a GUI. Doing devops type work on a GUI is from painful to impossible except in a few very niche areas.
"You assume that current restrictions will be maintained in the future. I don't think so."
I'll believe it when I see it. Apple in particular has no incentive to change. They love all that app store revenue, and they also have no incentive to make iOS a PC competitor since it would cannibalize their Mac platform sales.
Then there's the fact that the security problems that the app store model avoids have not actually been solved. Decouple mobile from app stores and you'll have a malware explosion.
Mobile is just a new platform. It's fantastic for a lot of things the old platforms aren't good at, but it's not going to displace old ones except at the edges. It's no more likely to displace the PC than it is to displace the server. What we're seeing is a filling-in and diversification of computing, not a displacement story.
I was one of those in the past, now it is just obvious, just look at the number of mobile devices out there compared to PCs. The fact that you don't like it does not make it less true.
Old people said the same about the command line, it was never going to be replaced for real work.
You assume that current restrictions will be maintained in the future. I don't think so.
Apple was right and created a product useful for many common people. Programmers and power users believed that it was not necessary because they were fine and frankly because knowledge gave them power over them.
I am using Ubuntu on a tablet and I like it. It is coming slowly but it will be possible to create much more content on tablets that on pcs.