Traditional desktop interfaces will survive, but they will survive in the same way that, say, Emacs survives -- as a niche product for that tiny market segment, not as the default way the Teeming Millions interact with their personal tech.
We should strive to support open protocols instead of closed APIs which are controlled by single companies.
Then everybody can use whatever User Interface they prefer and everbody can come up with new User Interfaces any time.
The AIM/ICQ/MSN vs. XMPP world illustrates this principle. Even if someone supports the closed protocols with a multi protocol client, the support eventually gets deliberately broken by the controlling party.
Protocols are way more important than the currently popular implementation of it.
Hm, but only as long as the saturation of "computers" is increasing rapidly. If you were to focus on a developed country with good smart phone penetration, I think it's possible that the percentage of coders is increasing as old people die and young people take to new technology more readily. I guess maybe it depends on where you draw the line between power user/script kiddie/programmer.
I doubt this statement. The number of people that write code is bound to increase in the future, not become smaller. And that has (among other things) to do with mobile devices getting cheaper and more capable. And generally with further increase of automation / software complexity. And with more people that want to be producers instead of consumers in the computer age...