You have to say why it will decline. You have to say whether it will be replaced, and if so by what. You have to present your reasoning and justify it.
Microsoft's then CTO presented his reasoning and justified it. So should you.
(And if you're going to whine that you were just making a joke? No. You were spewing a cheap little piece of cynicism.)
The memo is extremely vague about what it is predicting. It's basically agreeing with Sun ("the network is the computer" (c) 1984) / Larry Ellison ("Network Computer") / etc. - that something networked will outflank PCs.
But that's a prediction heavily dependent on timing (both those concepts failed to take off) and IMO misses what actually got the next generation of computing to take off (wireless networking, high-res screens and capacitive touch) and it also misses what is the main thrust of the next generation, mobility rather than connectedness.
He is right on target. Hindsight is 20/20, and it is an illusion that MS CTO had any deep insight.
People are predicting that mobile devices will be replaced by implants, or one of the many alternatives currently being prototyped, for reasons trivially linked to the relative strengths of the replacement. Check out Engadget and similar outlets for such predictions, they are dime a dozen. Imagine one of those articles nailing it; if you don't look at the other crap on Engadget, it will look like they actually knew what they were talking about.
Tablet is just a "smartphone" with a bigger screen. So it will be replaced by the "smartphone" when wireless display tech is both direction, i.e. display and input. In future, when I need to write/read a book, I bring out a foldable LCD display, "airplay" connect to it with my "smartphone" (Siri hit the screen please!). Or go to a meeting room with such screen, airplay to it to present my ideas. Or in StarBuck, pull out the LCD screen on the table, and airplay to it. Or the screen might have Kinect like sensor so I can interact with it like Minority Report. Or the screen might be by a corner of my glass (Google glass), so I can "airplay" to it. All this from my "smartphone" device hidden in my pocket. By then screen is needed less due to Siri version X, as most interaction and info search is by voice. For x-Apple people, just substitute Siri/AirPlay with similar tech names.
Hmmm ... This could be an interesting HN topic by itself. I think the most obvious answers are wearable computing, brain-machine interfaces (not implants) and vocal/sub-vocal input. Practical and common implants seem further than 15 years away to me.
