I can only see it as a viable desktop replacement for people that consume, rather than create. the ipod, ipad, android phones, etc. are data consumers- you read books, you read websites, etc. But the task of creation using these devices is unweildy, slow, and essentially discourages it; first you have smart-dumb features like "autocorrect" which can tuna your riding into nun cents, but you also have the fact that the screens are so small and difficult to use in the same manner as a keyboard & mouse.
Thing is this problem isn't really solved by just having an attachable keyboard because the system is designed as a device for consuming content anyway.
My point is, I guess for most people- who don't really create content, but instead use it- watch youtube, maybe write short E-mails, etc. It might work, and in fact most people have practically replaced their traditional desktop activities with portable devices. But it won't work in the same way for people that create said content.
